(c) by Christopher Sima /
e-mail: sima@isis.wu-wien.ac.at
This Texinfo manual describes PERL, the Practical Extraction and Report Language. The manual is, currently, mainly a conversion of Larry Wall's original unix-style man page into Texinfo format. In the future, new sections will be added, such as tutorial sections and more examples.
The Texinfo version of the perl manual is maintained and distributed by Jeff Kellem. His electronic mail address is composer@Beyond.Dreams.ORG. There is a mailing list for discussion of the Texinfo version of the perl manual and a mailing address for reporting bugs in this version of the manual. They are:
Mailing Address What The Address Is For perl-manual-request@Beyond.Dreams.ORG administrivia (add/drop requests) perl-manual@Beyond.Dreams.ORG discussion of the Texinfo perl manual bug-perl-manual@Beyond.Dreams.ORG reporting bugs in the perl manual
If you would like to join the discussion of the perl manual, send a note to
perl-manual-request@Beyond.Dreams.ORG
The latest edition of the Texinfo version of the Perl manual is available via anonymous ftp from:
ftp.dreams.orgin the
/pub/perl-manualdirectory.
Copyright (C) 1989 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
The license agreements of most software companies try to keep users at the mercy of those companies. By contrast, our General Public License is intended to guarantee your freedom to share and change free software--to make sure the software is free for all its users. The General Public License applies to the Free Software Foundation's software and to any other program whose authors commit to using it. You can use it for your programs, too.
When we speak of free software, we are referring to freedom, not price. Specifically, the General Public License is designed to make sure that you have the freedom to give away or sell copies of free software, that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of a such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must tell them their rights.
We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
The precise terms and conditions for copying, distribution and modification follow.
If you develop a new program, and you want it to be of the greatest possible use to humanity, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does. Copyright (C) 19yy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 1, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (a program to direct compilers to make passes at assemblers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
That's all there is to it!
[ Note: The following is from the author of Perl, Larry Wall. ]
My interpretation of the GNU General Public License is that no Perl script falls under the terms of the License unless you explicitly put said script under the terms of the License yourself. Furthermore, any object code linked with uperl.o does not automatically fall under the terms of the License, provided such object code only adds definitions of subroutines and variables, and does not otherwise impair the resulting interpreter from executing any standard Perl script. I consider linking in C subroutines in this manner to be the moral equivalent of defining subroutines in the Perl language itself. You may sell such an object file as proprietary provided that you provide or offer to provide the Perl source, as specified by the GNU General Public License. (This is merely an alternate way of specifying input to the program.) You may also sell a binary produced by the dumping of a running Perl script that belongs to you, provided that you provide or offer to provide the Perl source as specified by the License. (The fact that a Perl interpreter and your code are in the same binary file is, in this case, a form of mere aggregation.) This is my interpretation of the License. If you still have concerns or difficulties understanding my intent, feel free to contact me.
Perl is an interpreted language optimized for scanning arbitrary
text files, extracting information from those text files, and printing
reports based on that information. It's also a good language for many
system management tasks. The language is intended to be practical (easy
to use, efficient, complete) rather than beautiful (tiny, elegant,
minimal). It combines (in the author's opinion, anyway) some of the
best features of C, sed, awk, and sh, so
people familiar with those languages should have little difficulty with
it. (Language historians will also note some vestiges of csh,
Pascal, and even BASIC-PLUS.) Expression syntax
corresponds quite closely to C expression syntax. Unlike most Unix
utilities, perl does not arbitrarily limit the size of your
data--if you've got the memory, perl can slurp in your whole
file as a single string. Recursion is of unlimited depth. And the hash
tables used by associative arrays grow as necessary to prevent degraded
performance. Perl uses sophisticated pattern matching techniques
to scan large amounts of data very quickly. Although optimized for
scanning text, perl can also deal with binary data, and can make
dbm files look like associative arrays (where dbm is available). Setuid
perl scripts are safer than C programs through a dataflow tracing
mechanism which prevents many stupid security holes. If you have a
problem that would ordinarily use sed or awk or sh,
but it exceeds their capabilities or must run a little faster, and you
don't want to write the silly thing in C, then perl may be for
you. There are also translators to turn your sed and awk
scripts into perl scripts. OK, enough hype.
Upon startup, perl looks for your script in one of the following places:
stdin script you
must explicitly specify a `-' for the script name.After locating your script, perl compiles it to an internal form. If the script is syntactically correct, it is executed.
Note: on first reading this section may not make much sense to you. It's here at the front for easy reference.
A single-character option may be combined with the following option, if any. This is particularly useful when invoking a script using the `#!' construct which only allows one argument. Example:
#!/usr/bin/perl -spi.bak # same as -s -p -i.bak ...
Options include:
find
which can print filenames terminated by the null character, you can say
this:
find . -name '*.bak' -print0 | perl -n0e unlinkThe special value `00' will cause Perl to slurp files in paragraph mode. The value `0777' will cause Perl to slurp files whole since there is no legal character with that value.
perl -ane 'print pop(@F), "\n";'is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
perl -p -i.bak -e "s/foo/bar/;" ...is the same as using the script:
#!/usr/bin/perl -pi.bak s/foo/bar/;which is equivalent to
#!/usr/bin/perl
while (<>) {
if ($ARGV ne $oldargv) {
rename($ARGV, $ARGV . '.bak');
open(ARGVOUT, ">$ARGV");
select(ARGVOUT);
$oldargv = $ARGV;
}
s/foo/bar/;
}
continue {
print; # this prints to original filename
}
select(STDOUT);
except that the `-i' form doesn't need to compare `$ARGV' to
`$oldargv' to know when the filename has changed. It does, however,
use `ARGVOUT' for the selected filehandle. Note that `STDOUT'
is restored as the default output filehandle after the loop.
You can use eof to locate the end of each input file, in case you
want to append to each file, or reset line numbering
(see section Input/Output, for an example).
perl -lpe 'substr($_, 80) = ""'Note that the assignment
$\ = $/ is done when the switch is
processed, so the input record separator can be different than the
output record separator if the `-l' switch is followed by a
`-0' switch:
gnufind / -print0 | perl -ln0e 'print "found $_" if -p'This sets `$\' to newline and then sets `$/' to the null character.
sed -n or awk:
while (<>) {
... # your script goes here
}
Note that the lines are not printed by default. See `-p'
option to have lines printed. Here is an efficient way to delete all
files older than a week:
[ before version 4.003 ]
find . -mtime +7 -print | perl -ne 'chop;unlink;'[ version 4.003 and beyond ]
find . -mtime +7 -print | perl -nle 'unlink;'This is faster than using the `-exec' switch of find because you don't have to start a process on every filename found.
sed:
while (<>) {
... # your script goes here
} continue {
print;
}
Note that the lines are printed automatically. To suppress printing use
the `-n' switch. A `-p' overrides a `-n' switch.
if,
else or define.)
#!/usr/bin/perl -s
if ($xyz) { print "true\n"; }
#!/usr/bin/perl
eval "exec /usr/bin/perl -S $0 $*"
if $running_under_some_shell;
The system ignores the first line and feeds the script to
`/bin/sh', which proceeds to try to execute the perl script
as a shell script. The shell executes the second line as a normal shell
command, and thus starts up the perl interpreter. On some
systems `$0' doesn't always contain the full pathname, so the
`-S' tells perl to search for the script if necessary.
After perl locates the script, it parses the lines and ignores
them because the variable `$running_under_some_shell' is never
true. A better construct than `$*' would be `${1+"$@"}',
which handles embedded spaces and such in the filenames, but doesn't
work if the script is being interpreted by csh. In order to
start up sh rather than csh, some systems may have to
replace the `#!' line with a line containing just a colon, which
will be politely ignored by perl. Other systems can't control
that, and need a totally devious construct that will work under any of
csh, sh or perl, such as the following:
eval '(exit $?0)' && eval 'exec /usr/bin/perl -S $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -S $0 $argv:q'
if 0;
undump program (not supplied). This speeds startup at the
expense of some disk space (which you can minimize by stripping the
executable). (Still, a "hello world" executable comes out to about
200K on my machine.) If you are going to run your executable as a
set-id program then you should probably compile it using taintperl
rather than normal perl. If you want to execute a portion of your
script before dumping, use the dump operator instead. Note:
availability of undump is platform specific and may not be
available for a specific port of perl.
Perl has three data types: scalars, arrays of scalars, and associative arrays of scalars. Normal arrays are indexed by number, and associative arrays by string.
The interpretation of operations and values in perl sometimes depends on the requirements of the context around the operation or value. There are three major contexts: string, numeric and array. Certain operations return array values in contexts wanting an array, and scalar values otherwise. (If this is true of an operation it will be mentioned in the documentation for that operation.) Operations which return scalars don't care whether the context is looking for a string or a number, but scalar variables and values are interpreted as strings or numbers as appropriate to the context. A scalar is interpreted as TRUE in the boolean sense if it is not the null string or 0. Booleans returned by operators are 1 for TRUE and 0 or '' (the null string [two single right quotes]) for FALSE.
There are actually two varieties of null strings: defined and
undefined. Undefined null strings are returned when there is no
real value for something, such as when there was an error, or at end of
file, or when you refer to an uninitialized variable or element of an
array. An undefined null string may become defined the first time you
access it, but prior to that you can use the defined() operator
to determine whether the value is defined or not.
References to scalar variables always begin with `$', even when referring to a scalar that is part of an array. Thus:
$days # a simple scalar variable
$days[28] # 29th element of array @days
$days{'Feb'} # one value from an associative array
$#days # last index of array @days
but entire arrays or array slices are denoted by `@':
@days # ($days[0], $days[1],... $days[n])
@days[3,4,5] # same as @days[3..5]
@days{'a','c'} # same as ($days{'a'},$days{'c'})
and entire associative arrays are denoted by `%':
%days # (key1, val1, key2, val2 ...)
Any of these eight constructs may serve as an lvalue, that is, may be
assigned to. (It also turns out that an assignment is itself an lvalue
in certain contexts--see examples under s, tr and
chop.) Assignment to a scalar evaluates the righthand side in a
scalar context, while assignment to an array or array slice evaluates
the righthand side in an array context.
You may find the length of array `@days' by evaluating
`$#days', as in csh. (Actually, it's not the length of the
array, it's the subscript of the last element, since there is
(ordinarily) a 0th element.) Assigning to `$#days' changes the
length of the array. Shortening an array by this method does not
actually destroy any values. Lengthening an array that was previously
shortened recovers the values that were in those elements. You can also
gain some measure of efficiency by preextending an array that is going
to get big. (You can also extend an array by assigning to an element
that is off the end of the array. This differs from assigning to
`$#whatever' in that intervening values are set to null rather than
recovered.) You can truncate an array down to nothing by assigning the
null list `()' to it. The following are exactly equivalent:
@whatever = (); $#whatever = $[ - 1;
If you evaluate an array in a scalar context, it returns the length of the array. The following is always true:
scalar(@whatever) == $#whatever - $[ + 1;
If you evaluate an associative array in a scalar context, it returns a value which is true if and only if the array contains any elements. (If there are any elements, the value returned is a string consisting of the number of used buckets and the number of allocated buckets, separated by a slash.)
Multi-dimensional arrays are not directly supported, but see the discussion of the `$;' variable later for a means of emulating multiple subscripts with an associative array. You could also write a subroutine to turn multiple subscripts into a single subscript.
Every data type has its own namespace. You can, without fear of
conflict, use the same name for a scalar variable, an array, an
associative array, a filehandle, a subroutine name, and/or a label.
Since variable and array references always start with `$',
`@', or `%', the reserved words aren't in
fact reserved with respect to variable names. (They ARE
reserved with respect to labels and filehandles, however, which don't
have an initial special character. Hint: you could say
open(LOG,'logfile') rather than open(log,'logfile').
Using uppercase filehandles also improves readability and protects you
from conflict with future reserved words.) Case IS
significant---`FOO', `Foo' and `foo' are all different
names. Names which start with a letter may also contain digits and
underscores. Names which do not start with a letter are limited to one
character, e.g. `$%' or `$$'. (Most of the one character
names have a predefined significance to perl. More
later.)
Numeric literals are specified in any of the usual floating point or integer formats:
12345 12345.67 .23E-10 0xffff # hex 0377 # octal 4_294_967_296
String literals are delimited by either single or double quotes. They work much like shell quotes: double-quoted string literals are subject to backslash and variable substitution; single-quoted strings are not (except for \' and \\). The usual backslash rules apply for making characters such as newline, tab, etc., as well as some more exotic forms:
\t tab \n newline \r return \f form feed \b backspace \a alarm (bell) \e escape \033 octal char \x1b hex char \c[ control char \l lowercase next char \u uppercase next char \L lowercase till \E \U uppercase till \E \E end case modification
You can also embed newlines directly in your strings, i.e. they can end on a different line than they begin. This is nice, but if you forget your trailing quote, the error will not be reported until perl finds another line containing the quote character, which may be much further on in the script. Variable substitution inside strings is limited to scalar variables, normal array values, and array slices. (In other words, identifiers beginning with `$' or `@', followed by an optional bracketed expression as a subscript.) The following code segment prints out `The price is $100.'
$Price = '$100'; # not interpreted print "The price is $Price.\n"; # interpreted
Note that you can put curly brackets around the identifier to delimit it from following alphanumerics. Also note that a single quoted string must be separated from a preceding word by a space, since single quote is a valid character in an identifier. See section Packages, for more info.
Two special literals are `__LINE__' and `__FILE__', which represent the current line number and filename at that point in your program. They may only be used as separate tokens; they will not be interpolated into strings. In addition, the token `__END__' may be used to indicate the logical end of the script before the actual end of file. Any following text is ignored, but may be read via the `DATA' filehandle. (The `DATA' filehandle may read data only from the main script, but not from any required file or evaluated string.) The two control characters ^D and ^Z are synonyms for `__END__'.
A word that doesn't have any other interpretation in the grammar will be treated as if it had single quotes around it. For this purpose, a word consists only of alphanumeric characters and underline, and must start with an alphabetic character. As with filehandles and labels, a bare word that consists entirely of lowercase letters risks conflict with future reserved words, and if you use the `-w' switch, perl will warn you about any such words.
Array values are interpolated into double-quoted strings by joining all the elements of the array with the delimiter specified in the `$"' variable, space by default. (Since in versions of perl prior to 3.0 the `@' character was not a metacharacter in double-quoted strings, the interpolation of `@array', `$array[EXPR]', `@array[LIST]', `$array{EXPR}', or `@array{LIST}' only happens if array is referenced elsewhere in the program or is predefined.) The following are equivalent:
$temp = join($",@ARGV); system "echo $temp"; system "echo @ARGV";
Within search patterns (which also undergo double-quotish substitution) there is a bad ambiguity: Is `/$foo[bar]/' to be interpreted as `/${foo}[bar]/' (where `[bar]' is a character class for the regular expression) or as `/${foo[bar]}/' (where `[bar]' is the subscript to array `@foo')? If `@foo' doesn't otherwise exist, then it's obviously a character class. If `@foo' exists, perl takes a good guess about `[bar]', and is almost always right. If it does guess wrong, or if you're just plain paranoid, you can force the correct interpretation with curly brackets as above.
A line-oriented form of quoting is based on the shell here-is syntax. Following a `<<' you specify a string to terminate the quoted material, and all lines following the current line down to the terminating string are the value of the item. The terminating string may be either an identifier (a word), or some quoted text. If quoted, the type of quotes you use determines the treatment of the text, just as in regular quoting. An unquoted identifier works like double quotes. There must be no space between the `<<' and the identifier. (If you put a space it will be treated as a null identifier, which is valid, and matches the first blank line--see Merry Christmas example below.) The terminating string must appear by itself (unquoted and with no surrounding whitespace) on the terminating line.
print <<EOF; # same as above
The price is $Price.
EOF
print <<"EOF"; # same as above
The price is $Price.
EOF
print << x 10; # null identifier is delimiter
Merry Christmas!
print <<`EOC`; # execute commands
echo hi there
echo lo there
EOC
print <<foo, <<bar; # you can stack them
I said foo.
foo
I said bar.
bar
Array literals are denoted by separating individual values by commas, and enclosing the list in parentheses:
(LIST)
In a context not requiring an array value, the value of the array literal is the value of the final element, as in the C comma operator. For example,
@foo = ('cc', '-E', $bar);
assigns the entire array value to array foo, but
$foo = ('cc', '-E', $bar);
assigns the value of variable bar to variable foo. Note that the value of an actual array in a scalar context is the length of the array; the following assigns to `$foo' the value 3:
@foo = ('cc', '-E', $bar);
$foo = @foo; # $foo gets 3
You may have an optional comma before the closing parenthesis of an array literal, so that you can say:
@foo = (
1,
2,
3,
);
When a LIST is evaluated, each element of the list is evaluated in an array context, and the resulting array value is interpolated into LIST just as if each individual element were a member of LIST. Thus arrays lose their identity in a LIST--the list
(@foo,@bar,&SomeSub)
contains all the elements of `@foo' followed by all the elements of `@bar', followed by all the elements returned by the subroutine named `SomeSub'.
A list value may also be subscripted like a normal array. Examples:
$time = (stat($file))[8]; # stat returns array value
$digit = ('a','b','c','d','e','f')[$digit-10];
return (pop(@foo),pop(@foo))[0];
Array lists may be assigned to if and only if each element of the list is an lvalue:
($a, $b, $c) = (1, 2, 3);
($map{'red'}, $map{'blue'}, $map{'green'}) = (0x00f, 0x0f0, 0xf00);
The final element may be an array or an associative array:
($a, $b, @rest) = split; local($a, $b, %rest) = @_;
You can actually put an array anywhere in the list, but the first array
in the list will soak up all the values, and anything after it will get
a null value. This may be useful in a local().
An associative array literal contains pairs of values to be interpreted as a key and a value:
# same as map assignment above
%map = ('red',0x00f,'blue',0x0f0,'green',0xf00);
Array assignment in a scalar context returns the number of elements produced by the expression on the right side of the assignment:
$x = (($foo,$bar) = (3,2,1)); # set $x to 3, not 2
There are several other pseudo-literals that you should know about. If
a string is enclosed by backticks (grave accents), it first undergoes
variable substitution just like a double quoted string. It is then
interpreted as a command, and the output of that command is the value of
the pseudo-literal, like in a shell. In a scalar context, a single
string consisting of all the output is returned. In an array context,
an array of values is returned, one for each line of output. (You can
set `$/' to use a different line terminator.) The command is
executed each time the pseudo-literal is evaluated. The status value of
the command is returned in `$?' (See section Predefined Names, for the
interpretation of `$?'). Unlike in csh, no translation is
done on the return data--newlines remain newlines. Unlike in any of
the shells, single quotes do not hide variable names in the command from
interpretation. To pass a `$' through to the shell you need to
hide it with a backslash.
Evaluating a filehandle in angle brackets yields the next line from that
file (newline included, so it's never false until EOF, at which time the
undefined value is returned). Ordinarily you must assign that value to
a variable, but there is one situation where an automatic assignment
happens. If (and only if) the input symbol is the only thing inside the
conditional of a while loop, the value is automatically assigned
to the variable `$_'. (This may seem like an odd thing to you, but
you'll use the construct in almost every perl script you write.)
Anyway, the following lines are equivalent to each other:
while ($_ = <STDIN>) { print; }
while (<STDIN>) { print; }
for (;<STDIN>;) { print; }
print while $_ = <STDIN>;
print while <STDIN>;
The filehandles `STDIN', `STDOUT' and `STDERR' are
predefined. (The filehandles `stdin', `stdout' and
`stderr' will also work except in packages, where they would be
interpreted as local identifiers rather than global.) Additional
filehandles may be created with the open function.
If a `<FILEHANDLE>' is used in a context that is looking for an array, an array consisting of all the input lines is returned, one line per array element. It's easy to make a LARGE data space this way, so use with care.
The null filehandle `<>' is special and can be used to emulate the
behavior of sed and awk. Input from `<>' comes either
from standard input, or from each file listed on the command line. Here's
how it works: the first time `<>' is evaluated, the `ARGV' array
is checked, and if it is null, `$ARGV[0]' is set to `-', which
when opened gives you standard input. The `ARGV' array is then
processed as a list of filenames. The loop
while (<>) {
... # code for each line
}
is equivalent to the following Perl-like pseudo code:
unshift(@ARGV, '-') if $#ARGV < $[;
while ($ARGV = shift) {
open(ARGV, $ARGV);
while (<ARGV>) {
... # code for each line
}
}
except that it isn't as cumbersome to say, and will actually work. It really does shift array `ARGV' and put the current filename into variable `ARGV'. It also uses filehandle `ARGV' internally---`<>' is just a synonym for `<ARGV>', which is magical. (The pseudo code above doesn't work because it treats `<ARGV>' as non-magical.)
You can modify `@ARGV' before the first `<>' as long as the
array ends up containing the list of filenames you really want.
Line numbers (`$.') continue as if the input was one big happy
file. (But see example under eof for how to reset line numbers
on each file.)
If you want to set `@ARGV' to your own list of files, go right ahead. If you want to pass switches into your script, you can put a loop on the front like this:
while ($_ = $ARGV[0], /^-/) {
shift;
last if /^--$/;
/^-D(.*)/ && ($debug = $1);
/^-v/ && $verbose++;
... # other switches
}
while (<>) {
... # code for each line
}
The `<>' symbol will return FALSE only once. If you call it again after this it will assume you are processing another `@ARGV' list, and if you haven't set `@ARGV', will input from `STDIN'.
If the string inside the angle brackets is a reference to a scalar variable (e.g. `<$foo>'), then that variable contains the name of the filehandle to input from.
If the string inside angle brackets is not a filehandle, it is interpreted as a filename pattern to be globbed, and either an array of filenames or the next filename in the list is returned, depending on context. One level of `$' interpretation is done first, but you can't say `<$foo>' because that's an indirect filehandle as explained in the previous paragraph. You could insert curly brackets to force interpretation as a filename glob: `<${foo}>'. Example:
while (<*.c>) {
chmod 0644, $_;
}
is equivalent to
open(foo, "echo *.c | tr -s ' \t\r\f' '\\012\\012\\012\\012'|");
while (<foo>) {
chop;
chmod 0644, $_;
}
In fact, it's currently implemented that way. (Which means it will not work on filenames with spaces in them unless you have `/bin/csh' on your machine.) Of course, the shortest way to do the above is:
chmod 0644, <*.c>;
A perl script consists of a sequence of declarations and
commands. The only things that need to be declared in perl are
report formats and subroutines. See the sections below for more
information on those declarations. All uninitialized user-created
objects are assumed to start with a null or 0 value until they are
defined by some explicit operation such as assignment. The sequence of
commands is executed just once, unlike in sed and awk
scripts, where the sequence of commands is executed for each input line.
While this means that you must explicitly loop over the lines of your
input file (or files), it also means you have much more control over
which files and which lines you look at. (Actually, I'm lying--it is
possible to do an implicit loop with either the `-n' or `-p'
switch.)
A declaration can be put anywhere a command can, but has no effect on the execution of the primary sequence of commands--declarations all take effect at compile time. Typically all the declarations are put at the beginning or the end of the script.
Perl is, for the most part, a free-form language. (The only exception to this is format declarations, for fairly obvious reasons.) Comments are indicated by the `#' character, and extend to the end of the line. If you attempt to use `/* */' C comments, it will be interpreted either as division or pattern matching, depending on the context. So don't do that.
In perl, a sequence of commands may be treated as one command by enclosing it in curly brackets. We will call this a BLOCK.
The following compound commands may be used to control flow:
if (EXPR) BLOCK if (EXPR) BLOCK else BLOCK if (EXPR) BLOCK elsif (EXPR) BLOCK ... else BLOCK LABEL while (EXPR) BLOCK LABEL while (EXPR) BLOCK continue BLOCK LABEL for (EXPR; EXPR; EXPR) BLOCK LABEL foreach VAR (ARRAY) BLOCK LABEL BLOCK continue BLOCK
Note that, unlike C and Pascal, these are defined in terms of BLOCKs, not statements. This means that the curly brackets are required---no dangling statements allowed. If you want to write conditionals without curly brackets there are several other ways to do it. The following all do the same thing:
if (!open(foo)) { die "Can't open $foo: $!"; }
die "Can't open $foo: $!" unless open(foo);
open(foo) || die "Can't open $foo: $!"; # foo or bust!
open(foo) ? 'hi mom' : die "Can't open $foo: $!";
# a bit exotic, that last one
The if statement is straightforward. Since BLOCKs are always
bounded by curly brackets, there is never any ambiguity about which
if an else goes with. If you use unless in place
of if, the sense of the test is reversed.
The while statement executes the block as long as the expression
is true (does not evaluate to the null string or 0). The LABEL is
optional, and if present, consists of an identifier followed by a colon.
The LABEL identifies the loop for the loop control statements
next, last, and redo (see below). If there is a
continue BLOCK, it is always executed just before the conditional
is about to be evaluated again, similarly to the third part of a
for loop in C. Thus it can be used to increment a loop variable,
even when the loop has been continued via the next statement
(similar to the C continue statement).
If the word while is replaced by the word until, the sense
of the test is reversed, but the conditional is still tested before the
first iteration.
In either the if or the while statement, you may replace
`(EXPR)' with a BLOCK, and the conditional is true if the value of
the last command in that block is true.
The for loop works exactly like the corresponding while
loop:
for ($i = 1; $i < 10; $i++) {
...
}
is the same as
$i = 1;
while ($i < 10) {
...
} continue {
$i++;
}
The foreach loop iterates over a normal array value and sets the
variable VAR to be each element of the array in turn. The
variable is implicitly local to the loop, and regains its former value
upon exiting the loop. The foreach keyword is actually identical
to the for keyword, so you can use foreach for readability
or for for brevity. If VAR is omitted, `$_' is set to
each value. If ARRAY is an actual array (as opposed to an
expression returning an array value), you can modify each element of the
array by modifying VAR inside the loop. Examples:
for (@ary) { s/foo/bar/; }
foreach $elem (@elements) {
$elem *= 2;
}
for ((10,9,8,7,6,5,4,3,2,1,'BOOM')) {
print $_, "\n"; sleep(1);
}
for (1..15) { print "Merry Christmas\n"; }
foreach $item (split(/:[\\\n:]*/, $ENV{'TERMCAP'})) {
print "Item: $item\n";
}
The BLOCK by itself (labeled or not) is equivalent to a loop that
executes once. Thus you can use any of the loop control statements in
it to leave or restart the block. The continue block is
optional. This construct is particularly nice for doing case
structures.
foo: {
if (/^abc/) { $abc = 1; last foo; };
if (/^def/) { $def = 1; last foo; };
if (/^xyz/) { $xyz = 1; last foo; };
$nothing = 1;
}
There is no official switch statement in perl, because there are already several ways to write the equivalent. In addition to the above, you could write:
foo: {
$abc = 1, last foo if /^abc/;
$def = 1, last foo if /^def/;
$xyz = 1, last foo if /^xyz/;
$nothing = 1;
}
or
foo: {
/^abc/ && do { $abc = 1; last foo; }
/^def/ && do { $def = 1; last foo; }
/^xyz/ && do { $xyz = 1; last foo; }
$nothing = 1;
}
or
foo: {
/^abc/ && ($abc = 1, last foo);
/^def/ && ($def = 1, last foo);
/^xyz/ && ($xyz = 1, last foo);
$nothing = 1;
}
or even
if (/^abc/)
{ $abc = 1; }
elsif (/^def/)
{ $def = 1; }
elsif (/^xyz/)
{ $xyz = 1; }
else
{$nothing = 1;}
As it happens, these are all optimized internally to a switch structure,
so perl jumps directly to the desired statement, and you needn't worry
about perl executing a lot of unnecessary statements when you have a
string of 50 elsifs, as long as you are testing the same simple
scalar variable using `==', `eq', or pattern matching as
above. (If you're curious as to whether the optimizer has done this for
a particular case statement, you can use the `-D1024' switch to
list the syntax tree before execution.)
The only kind of simple statement is an expression evaluated for its side effects. Every simple statement must be terminated with a semicolon, unless it is the final statement in a block, in which case the semicolon is optional. (Semicolon is still encouraged there if the block takes up more than one line).
Any simple statement may optionally be followed by a single modifier, just before the terminating semicolon. The possible modifiers are:
if EXPR unless EXPR while EXPR until EXPR
The if and unless modifiers have the expected semantics.
The while and until modifiers also have the expected
semantics (conditional evaluated first), except when applied to a
do-BLOCK or a do-SUBROUTINE command, in which case the block executes
once before the conditional is evaluated. This is so that you can write
loops like:
do {
$_ = <STDIN>;
...
} until $_ eq ".\n";
(See the do operator below. Note also that the loop control
commands described later will NOT work in this construct, since
modifiers don't take loop labels. Sorry.)
Since perl expressions work almost exactly like C expressions, only the differences will be mentioned here.
Here's what perl has that C doesn't:
awk
behavior of using `==' for either string or numeric equality based
on the current form of the comparands, beware! You must be explicit
here.)
print '-' x 80; # print row of dashes print '-' x80; # illegal, x80 is identifier print "\t" x ($tab/8), ' ' x ($tab%8); # tab over @ones = (1) x 80; # an array of 80 1's @ones = (5) x @ones; # set all elements to 5
for (1..10) loops and for doing slice operations on
arrays.
In a scalar context, `..' returns a boolean value. The operator is
bistable, like a flip-flop, and emulates the line-range (comma) operator
of sed, awk, and various editors. Each `..' operator
maintains its own
boolean state. It is false as long as its left operand is false. Once
the left operand is true, the range operator stays true until the right
operand is true, AFTER which the range operator becomes false
again. (It doesn't become false till the next time the range operator
is evaluated. It can test the right operand and become false on the same
evaluation it became true (as in awk), but it still returns true
once. If you don't want it to test the right operand till the next
evaluation (as in sed), use three dots (...) instead of two.)
The right operand is not
evaluated while the operator is in the "false" state, and the left
operand is not evaluated while the operator is in the "true" state.
The
precedence is a little lower than `||' and `&&'. The value
returned is either the null string for false, or a sequence number
(beginning with 1) for true. The sequence number is reset for each
range encountered. The final sequence number in a range has the string
`E0' appended to it, which doesn't affect its numeric value, but
gives you something to search for if you want to exclude the endpoint.
You can exclude the beginning point by waiting for the sequence number
to be greater than 1. If either operand of scalar `..' is static,
that operand is implicitly compared to the `$.' variable, the
current line number. Examples:
As a scalar operator:
if (101 .. 200) { print; } # print 2nd hundred lines
next line if (1 .. /^$/); # skip header lines
s/^/> / if (/^$/ .. eof()); # quote body
As an array operator:
for (101 .. 200) { print; } # print $_ 100 times
@foo = @foo[$[ .. $#foo]; # an expensive no-op
@foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items
-r File is readable by effective uid/gid. -w File is writable by effective uid/gid. -x File is executable by effective uid/gid. -o File is owned by effective uid. -R File is readable by real uid/gid. -W File is writable by real uid/gid. -X File is executable by real uid/gid. -O File is owned by real uid. -e File exists. -z File has zero size. -s File has non-zero size (returns size). -f File is a plain file. -d File is a directory. -l File is a symbolic link. -p File is a named pipe (FIFO). -S File is a socket. -b File is a block special file. -c File is a character special file. -u File has setuid bit set. -g File has setgid bit set. -k File has sticky bit set. -t Filehandle is opened to a tty. -T File is a text file. -B File is a binary file (opposite of -T). -M Age of file in days when script started. -A Same for access time. -C Same for inode change time.The interpretation of the file permission operators `-r', `-R', `-w', `-W', `-x' and `-X' is based solely on the mode of the file and the uids and gids of the user. There may be other reasons you can't actually read, write or execute the file. Also note that, for the superuser, `-r', `-R', `-w' and `-W' always return 1, and `-x' and `-X' return 1 if any execute bit is set in the mode. Scripts run by the superuser may thus need to do a
stat() in order to determine the actual mode of the
file, or temporarily set the uid to something else.
Example:
while (<>) {
chop;
next unless -f $_; # ignore specials
...
}
Note that `-s/a/b/' does not do a negated substitution. Saying
`-exp($foo)' still works as expected, however--only single letters
following a minus are interpreted as file tests.
The `-T' and `-B' switches work as follows. The first block
or so of the file is examined for odd characters such as strange control
codes or metacharacters. If too many odd characters (>10%) are found,
it's a `-B' file, otherwise it's a `-T' file. Also, any file
containing null in the first block is considered a binary file. If
`-T' or `-B' is used on a filehandle, the current stdio buffer
is examined rather than the first block. Both `-T' and `-B'
return TRUE on a null file, or a file at EOF when testing a filehandle.
If any of the file tests (or either stat operator) are given the
special filehandle consisting of a solitary underline `_', then the
stat structure of the previous file test (or stat operator) is
used, saving a system call. (This doesn't work with `-t', and you
need to remember that lstat and `-l' will leave values in
the stat structure for the symbolic link, not the real file.) Example:
print "Can do.\n" if -r $a || -w _ || -x _; stat($filename); print "Readable\n" if -r _; print "Writable\n" if -w _; print "Executable\n" if -x _; print "Setuid\n" if -u _; print "Setgid\n" if -g _; print "Sticky\n" if -k _; print "Text\n" if -T _; print "Binary\n" if -B _;
Here is what C has that perl doesn't:
Like C, perl does a certain amount of expression evaluation at compile time, whenever it determines that all of the arguments to an operator are static and have no side effects. In particular, string concatenation happens at compile time between literals that don't do variable substitution. Backslash interpretation also happens at compile time. You can say:
'Now is the time for all' . "\n" . 'good men to come to.'
and this all reduces to one string internally.
The autoincrement operator has a little extra built-in magic to it. If you increment a variable that is numeric, or that has ever been used in a numeric context, you get a normal increment. If, however, the variable has only been used in string contexts since it was set, and has a value that is not null and matches the pattern `/^[a-zA-Z]*[0-9]*$/', the increment is done as a string, preserving each character within its range, with carry:
print ++($foo = '99'); # prints `100' print ++($foo = 'a0'); # prints `a1' print ++($foo = 'Az'); # prints `Ba' print ++($foo = 'zz'); # prints `aaa'
The autodecrement is not magical.
The range operator (in an array context) makes use of the magical autoincrement algorithm if the minimum and maximum are strings. You can say
@alphabet = ('A' .. 'Z');
to get all the letters of the alphabet, or
$hexdigit = (0 .. 9, 'a' .. 'f')[$num & 15];
to get a hexadecimal digit, or
@z2 = ('01' .. '31'); print @z2[$mday];
to get dates with leading zeros. (If the final value specified is not in the sequence that the magical increment would produce, the sequence goes until the next value would be longer than the final value specified.)
The `||' and `&&' operators differ from C's in that, rather than returning 0 or 1, they return the last value evaluated. Thus, a portable way to find out the home directory might be:
$home = $ENV{'HOME'} || $ENV{'LOGDIR'} ||
(getpwuid($<))[7] || die "You're homeless!\en";
Along with the literals and variables mentioned earlier, the operations in the following section can serve as terms in an expression. Some of these operations take a LIST as an argument. Such a list can consist of any combination of scalar arguments or array values; the array values will be included in the list as if each individual element were interpolated at that point in the list, forming a longer single-dimensional array value. Elements of the LIST should be separated by commas. If an operation is listed both with and without parentheses around its arguments, it means you can either use it as a unary operator or as a function call. To use it as a function call, the next token on the same line must be a left parenthesis. (There may be intervening white space.) Such a function then has highest precedence, as you would expect from a function. If any token other than a left parenthesis follows, then it is a unary operator, with a precedence depending only on whether it is a LIST operator or not. LIST operators have lowest precedence. All other unary operators have a precedence greater than relational operators but less than arithmetic operators. See section Precedence, for more info.
For operators that can be used in either a scalar or array context, failure is generally indicated in a scalar context by returning the undefined value, and in an array context by returning the null list. Remember though that THERE IS NO GENERAL RULE FOR CONVERTING A LIST INTO A SCALAR. Each operator decides which sort of scalar it would be most appropriate to return. Some operators return the length of the list that would have been returned in an array context. Some operators return the first value in the list. Some operators return the last value in the list. Some operators return a count of successful operations. In general, they do what you want, unless you want consistency.
exp($_).
oct().) If EXPR is omitted, uses `$_'.
$val = oct($val) if $val =~ /^0/;If EXPR is omitted, uses `$_'.
A An ascii string, will be space padded. a An ascii string, will be null padded. c A signed char value. C An unsigned char value. s A signed short value. S An unsigned short value. i A signed integer value. I An unsigned integer value. l A signed long value. L An unsigned long value. n A short in `network' order. N A long in `network' order. f A single-precision float in the native format. d A double-precision float in the native format. p A pointer to a string. v A short in `VAX' (little-endian) order. V A long in `VAX' (little-endian) order. x A null byte. X Back up a byte. @ Null fill to absolute position. u A uuencoded string. b A bit string (ascending bit order, like vec()). B A bit string (descending bit order). h A hex string (low nybble first). H A hex string (high nybble first).Each letter may optionally be followed by a number which gives a repeat count. With all types except `a', `A', `b', `B', `h', and `H', the pack function will gobble up that many values from the LIST. A `*' for the repeat count means to use however many items are left. The `a' and `A' types gobble just one value, but pack it as a string of length count, padding with nulls or spaces as necessary. (When unpacking, `A' strips trailing spaces and nulls, but `a' does not.) Likewise, the `b' and `B' fields pack a string that many bits long. The `h' and `H' fields pack a string that many nybbles long. Real numbers (floats and doubles) are in the native machine format only; due to the multiplicity of floating formats around, and the lack of a standard "network" representation, no facility for interchange has been made. This means that packed floating point data written on one machine may not be readable on another - even if both use IEEE floating point arithmetic (as the endian-ness of the memory representation is not part of the IEEE spec). Note that perl uses doubles internally for all numeric calculation, and converting from double to float back to double will lose precision (i.e. `unpack("f", pack("f", $foo))' will not in general equal `$foo'). Examples:
$foo = pack("cccc",65,66,67,68);
# foo eq "ABCD"
$foo = pack("c4",65,66,67,68);
# same thing
$foo = pack("ccxxcc",65,66,67,68);
# foo eq "AB\0\0CD"
$foo = pack("s2",1,2);
# "\1\0\2\0" on little-endian
# "\0\1\0\2" on big-endian
$foo = pack("a4","abcd","x","y","z");
# "abcd"
$foo = pack("aaaa","abcd","x","y","z");
# "axyz"
$foo = pack("a14","abcdefg");
# "abcdefg\0\0\0\0\0\0\0"
$foo = pack("i9pl", gmtime);
# a real struct tm (on my system anyway)
sub bintodec {
unpack("N", pack("B32", substr("0" x 32 . shift, -32)));
}
The same template may generally also be used in the unpack
function.
unpack does the reverse of pack: it takes a string
representing a structure and expands it out into an array value,
returning the array value. (In a scalar context, it merely returns the
first value produced.) The TEMPLATE has the same format as in the
pack function. Here's a subroutine that does substring:
sub substr {
local($what,$where,$howmuch) = @_;
unpack("x$where a$howmuch", $what);
}
and then there's
sub ord { unpack("c",$_[0]); }
In addition, you may prefix a field with a `%<number>' to indicate
that you want a <number>-bit checksum of the items instead of the items
themselves. Default is a 16-bit checksum. For example, the following
computes the same number as the System V sum program:
while (<>) {
$checksum += unpack("%16C*", $_);
}
$checksum %= 65536;
while (<>) {
chop; # avoid \n on last field
@array = split(/:/);
...
}
You can actually chop anything that's an lvalue, including an
assignment:
chop($cwd = `pwd`); chop($answer = <STDIN>);If you chop a list, each element is chopped. Only the value of the last chop is returned.
crypt() function in the C library.
Useful for checking the password file for lousy passwords. Only the
guys wearing white hats should do this.
index except that it returns the position of the
LAST occurrence of SUBSTR in STR. If POSITION
is specified, returns the last occurrence at or before that
position.
substr() function as an lvalue, in which case EXPR must be
an lvalue. If you assign something shorter than LEN, the string
will shrink, and if you assign something longer than LEN, the
string will grow to accommodate it. To keep the string the same length
you may need to pad or chop your value using sprintf().
foreach $key (keys %ARRAY) {
delete $ARRAY{$key};
}
(But it would be faster to use the reset command. Saying
`undef %ARRAY' is faster yet.)
each() after that will start iterating
again. The iterator can be reset only by reading all the elements from
the array. You must not modify the array while iterating over it.
There is a single iterator for each associative array, shared by all
each(), keys() and values() function calls in the
program. The following prints out your environment like the
printenv program, only in a different order:
while (($key,$value) = each %ENV) {
print "$key=$value\n";
}
See also keys() and values().
@foo = grep(!/^#/, @bar); # weed out commentsNote that, since `$_' is a reference into the array value, it can be used to modify the elements of the array. While this is useful and supported, it can cause bizarre results if the LIST is not a named array.
$_ = join(':', $login,$passwd,$uid,$gid,$gcos,$home,$shell);
See split function.
values() or each()
function produces (given that the associative array has not been
modified). Here is yet another way to print your environment:
@keys = keys %ENV;
@values = values %ENV;
while ($#keys >= 0) {
print pop(@keys), '=', pop(@values), "\n";
}
or how about sorted by key:
foreach $key (sort(keys %ENV)) {
print $key, '=', $ENV{$key}, "\n";
}
$tmp = $ARRAY[$#ARRAY--];If there are no elements in the array, returns the undefined value.
for $value (LIST) {
$ARRAY[++$#ARRAY] = $value;
}
but is more efficient.
unshift(), push() and pop(). shift() and
unshift() do the same thing to the left end of an array that
push() and pop() do to the right end.
<=> and
cmp operators are extremely useful in such routines.)
SUBROUTINE may be a scalar variable name, in which case the value
provides the name of the subroutine to use. In place of a
SUBROUTINE name, you can provide a BLOCK as an anonymous,
in-line sort subroutine.
In the interests of efficiency the normal calling code for subroutines
is bypassed, with the following effects: the subroutine may not be a
recursive subroutine, and the two elements to be compared are passed
into the subroutine not via `@_' but as `$a' and `$b'
(see example below). They are passed by reference so don't modify
`$a' and `$b'. Examples:
# sort lexically
@articles = sort @files;
# same thing, but with explicit sort routine
@articles = sort { $a cmp $b } @files;
# same thing in reversed order
@articles = sort { $b cmp $a } @files;
# sort numerically ascending
@articles = sort { $a <=> $b } @files;
# sort numerically descending
@articles = sort { $b <=> $a } @files;
# sort using explicit subroutine name
sub byage {
$age{$a} <=> $age{$b}; # presuming integers
}
@sortedclass = sort byage @class;
sub reverse { $b cmp $a; }
@harry = ('dog','cat','x','Cain','Abel');
@george = ('gone','chased','yz','Punished','Axed');
print sort @harry;
# prints AbelCaincatdogx
print sort reverse @harry;
# prints xdogcatCainAbel
print sort @george, 'to', @harry;
# prints AbelAxedCainPunishedcatchaseddoggonetoxyz
$[ == 0):
push(@a,$x,$y) splice(@a,$#x+1,0,$x,$y) pop(@a) splice(@a,-1) shift(@a) splice(@a,0,1) unshift(@a,$x,$y) splice(@a,0,0,$x,$y) $a[$x] = $y splice(@a,$x,1,$y);Example, assuming array lengths are passed before arrays:
sub aeq { # compare two array values
local(@a) = splice(@_,0,shift);
local(@b) = splice(@_,0,shift);
return 0 unless @a == @b; # same len?
while (@a) {
return 0 if pop(@a) ne pop(@b);
}
return 1;
}
if (&aeq($len,@foo[1..$len],0+@bar,@bar)) { ... }
pop() would do well to remember). A pattern
matching the null string (not to be confused with a null pattern
`//', which is just one member of the set of patterns matching a
null string) will split the value of EXPR into separate characters
at each point it matches that way. For example:
print join(':', split(/ */, 'hi there'));
produces the output `h:i:t:h:e:r:e'.
The LIMIT parameter can be used to partially split a line
($login, $passwd, $remainder) = split(/:/, $_, 3);(When assigning to a list, if LIMIT is omitted, perl supplies a LIMIT one larger than the number of variables in the list, to avoid unnecessary work. For the list above LIMIT would have been 4 by default. In time critical applications it behooves you not to split into more fields than you really need.) If the PATTERN contains parentheses, additional array elements are created from each matching substring in the delimiter.
split(/([,-])/,"1-10,20");produces the array value
(1,'-',10,',',20)The pattern /PATTERN/ may be replaced with an expression to specify patterns that vary at runtime. (To do runtime compilation only once, use `/$variable/o'.) As a special case, specifying a space (' ') will split on white space just as split with no arguments does, but leading white space does NOT produce a null first field. Thus, split(' ') can be used to emulate
awk's default behavior,
whereas `split(/ /)' will give you as many null initial fields as
there are leading spaces.
Example:
open(passwd, '/etc/passwd');
while (<passwd>) {
($login, $passwd, $uid, $gid, $gcos, $home, $shell)
= split(/:/);
...
}
(Note that `$shell' above will still have a newline on it. See
chop().) See also join.
shift. Or the opposite of a push,
depending on how you look at it. Prepends list to the front of the
array, and returns the number of elements in the new array.
unshift(ARGV, '-e') unless $ARGV[0] =~ /^-/;
keys() or
each() function would produce on the same array. See also
keys() and each().
$cnt = chmod 0755, 'foo', 'bar'; chmod 0755, @executables;
$cnt = chown $uid, $gid, 'foo', 'bar'; chown $uid, $gid, @filenames;Here's an example that looks up non-numeric uids in the passwd file:
print "User: ";
$user = <STDIN>;
chop($user);
print "Files: "
$pattern = <STDIN>;
chop($pattern);
open(pass, '/etc/passwd') || die "Can't open passwd: $!\n";
while (<pass>) {
($login,$pass,$uid,$gid) = split(/:/);
$uid{$login} = $uid;
$gid{$login} = $gid;
}
@ary = <${pattern}>; # get filenames
if ($uid{$user} eq '') {
die "$user not in passwd file";
}
else {
chown $uid{$user}, $gid{$user}, @ary;
}
require "fcntl.ph"; # probably /usr/local/lib/perl/fcntl.phfirst to get the correct function definitions. If `fcntl.ph' doesn't exist or doesn't have the correct definitions you'll have to roll your own, based on your C header files such as `<sys/fcntl.h>'. (There is a perl script called `h2ph' that comes with the perl kit which may help you in this.) Argument processing and value return works just like
ioctl below. Note
that fcntl will produce a fatal error if used on a machine that
doesn't implement `fcntl(2)'.
select(). If FILEHANDLE is an expression, the
value is taken as the name of the filehandle.
$LOCK_SH = 1;
$LOCK_EX = 2;
$LOCK_NB = 4;
$LOCK_UN = 8;
sub lock {
flock(MBOX,$LOCK_EX);
# and, in case someone appended
# while we were waiting...
seek(MBOX, 0, 2);
}
sub unlock {
flock(MBOX,$LOCK_UN);
}
open(MBOX, ">>/usr/spool/mail/$ENV{'USER'}")
|| die "Can't open mailbox: $!";
do lock();
print MBOX $msg,"\n\n";
do unlock();
stat() function, but stats a symbolic
link instead of the file the symbolic link points to. If symbolic links
are unimplemented on your system, a normal stat is done.
stat fails.
Typically used as follows:
($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,
$atime,$mtime,$ctime,$blksize,$blocks)
= stat($filename);
If stat is passed the special filehandle consisting of an
underline (`_'), no stat is done, but the current contents of the
stat structure from the last stat or filetest are returned.
Example:
if (-x $file && (($d) = stat(_)) && $d < 0) {
print "$file is executable NFS file\n";
}
(This only works on machines for which the device number is negative
under NFS.)
$symlink_exists = (eval 'symlink("","");', $@ eq '');
truncate
isn't implemented on your system.
$cnt = unlink 'a', 'b', 'c'; unlink @goners; unlink <*.bak>;Note: unlink will not delete directories unless you are superuser and the `-U' flag is supplied to perl. Even if these conditions are met, be warned that unlinking a directory can inflict damage on your filesystem. Use
rmdir instead.
#!/usr/bin/perl $now = time; utime $now, $now, @ARGV;
die.
opendir().
umask). If it succeeds
it returns 1, otherwise it returns 0 and sets `$!' (errno).
readdir(),
telldir(), seekdir(), rewinddir() and
closedir(). Returns true if successful. DIRHANDLEs have
their own namespace separate from FILEHANDLEs.
opendir(). If used in an array context, returns all the rest of
the entries in the directory. If there are no more entries, returns an
undefined value in a scalar context or a null list in an array
context.
readdir() routine on DIRHANDLE.
readdir() routine on
DIRHANDLE. POS must be a value returned by
telldir(). Has the same caveats about possible directory
compaction as the corresponding system library routine.
readdir() routines on
DIRHANDLE. Value may be given to seekdir() to access a
particular location in a directory. Has the same caveats about possible
directory compaction as the corresponding system library routine.
binmode has no effect
under Unix. If FILEHANDLE is an expression, the value is taken as
the name of the filehandle.
open.)
However, an explicit close on an input file resets the line counter
(`$.'), while the implicit close done by open does not.
Also, closing a pipe will wait for the process executing on the pipe to
complete, in case you want to look at the output of the pipe afterwards.
Closing a pipe explicitly also puts the status value of the command into
`$?'. Example:
open(OUTPUT, '|sort >foo'); # pipe to sort ... # print stuff to output close OUTPUT; # wait for sort to finish open(INPUT, 'foo'); # get sort's resultsFILEHANDLE may be an expression whose value gives the real filehandle name.
ungetc's it, so it is
not very useful in an interactive context.) An eof without an
argument returns the eof status for the last file read. Empty
parentheses `()' may be used to indicate the pseudo file formed of
the files listed on the command line, i.e. `eof()' is reasonable to
use inside a `while (<>)' loop to detect the end of only the last
file. Use `eof(ARGV)' or eof without the parentheses to
test EACH file in a `while (<>)' loop. Examples:
# insert dashes just before last line of last file
while (<>) {
if (eof()) {
print "--------------\n";
}
print;
}
# reset line numbering on each input file
while (<>) {
print "$.\t$_";
if (eof) { # Not eof().
close(ARGV);
}
}
open
returns non-zero upon success, the undefined value otherwise. If the open
involved a pipe, the return value happens to be the pid of the subprocess.
Examples:
$article = 100;
open article || die "Can't find article $article: $!\n";
while (<article>) {...
open(LOG, '>>/usr/spool/news/twitlog');
# (log is reserved)
open(article, "caesar <$article |");
# decrypt article
open(extract, "|sort >/tmp/Tmp$$");
# $$ is our process#
# process argument list of files along with any includes
foreach $file (@ARGV) {
do process($file, 'fh00'); # no pun intended
}
sub process {
local($filename, $input) = @_;
$input++; # this is a string increment
unless (open($input, $filename)) {
print STDERR "Can't open $filename: $!\n";
return;
}
while (<$input>) { # note the use of indirection
if (/^#include "(.*)"/) {
do process($1, $input);
next;
}
... # whatever
}
}
You may also, in the Bourne shell tradition, specify an EXPR
beginning with `>&', in which case the rest of the string is
interpreted as the name of a filehandle (or file descriptor, if numeric)
which is to be duped and opened. You may use `&' after `>',
`>>', `<', `+>', `+>>' and `+<'. The mode you
specify should match the mode of the original filehandle. Here is a
script that saves, redirects, and restores `STDOUT' and
`STDERR':
#!/usr/bin/perl open(SAVEOUT, ">&STDOUT"); open(SAVEERR, ">&STDERR"); open(STDOUT, ">foo.out") || die "Can't redirect stdout"; open(STDERR, ">&STDOUT") || die "Can't dup stdout"; select(STDERR); $| = 1; # make unbuffered select(STDOUT); $| = 1; # make unbuffered print STDOUT "stdout 1\n"; # this works for print STDERR "stderr 1\n"; # subprocesses too close(STDOUT); close(STDERR); open(STDOUT, ">&SAVEOUT"); open(STDERR, ">&SAVEERR"); print STDOUT "stdout 2\n"; print STDERR "stderr 2\n";If you open a pipe on the command `-', i.e. either `|-' or `-|', then there is an implicit fork done, and the return value of open is the pid of the child within the parent process, and 0 within the child process. (Use `defined($pid)' to determine if the
open was successful.) The filehandle behaves normally for the
parent, but i/o to that filehandle is piped from/to the
`STDOUT'/`STDIN' of the child process. In the child process
the filehandle isn't opened--i/o happens from/to the new `STDOUT'
or `STDIN'. Typically this is used like the normal piped
open when you want to exercise more control over just how the
pipe command gets executed, such as when you are running setuid, and
don't want to have to scan shell commands for metacharacters. The
following pairs are equivalent:
open(FOO, "|tr '[a-z]' '[A-Z]'"); open(FOO, "|-") || exec 'tr', '[a-z]', '[A-Z]'; open(FOO, "cat -n '$file'|"); open(FOO, "-|") || exec 'cat', '-n', $file;Explicitly closing any piped filehandle causes the parent process to wait for the child to finish, and returns the status value in `$?'. Note: on any operation which may do a fork, unflushed buffers remain unflushed in both processes, which means you may need to set `$|' to avoid duplicate output. The filename that is passed to open will have leading and trailing whitespace deleted. In order to open a file with arbitrary weird characters in it, it's necessary to protect any leading and trailing whitespace thusly:
$file =~ s#^(\s)#./$1#; open(FOO, "< $file\0");
select()).If LIST is also omitted, prints `$_' to `STDOUT'. To set
the default output channel to something other than `STDOUT' use the
select operation. Note that, because print takes a LIST,
anything in the LIST is evaluated in an array context, and any
subroutine that you call will have one or more of its expressions evaluated
in an array context. Also be careful not to follow the print
keyword with a left parenthesis unless you want the corresponding right
parenthesis to terminate the arguments to the print---interpose a
`+' or put parens around all the arguments.
undef if there was an error. SCALAR
will be grown or shrunk to the length actually read. An OFFSET
may be specified to place the read data at some other place than the
beginning of the string. This call is actually implemented in terms of
stdio's fread call. To get a true read system call,
see sysread.
fileno() and vec(), along these
lines:
$rin = $win = $ein = ''; vec($rin,fileno(STDIN),1) = 1; vec($win,fileno(STDOUT),1) = 1; $ein = $rin | $win;If you want to select on many filehandles you might wish to write a subroutine:
sub fhbits {
local(@fhlist) = split(' ',$_[0]);
local($bits);
for (@fhlist) {
vec($bits,fileno($_),1) = 1;
}
$bits;
}
$rin = &fhbits('STDIN TTY SOCK');
The usual idiom is:
($nfound,$timeleft) = select($rout=$rin, $wout=$win, $eout=$ein, $timeout);or to block until something becomes ready:
$nfound = select($rout=$rin, $wout=$win,
$eout=$ein, undef);
Any of the bitmasks can also be undef. The timeout, if
specified, is in seconds, which may be fractional. NOTE: not all
implementations are capable of returning the `$timeleft'. If not,
they always return `$timeleft' equal to the supplied
`$timeout'.
fseek() call of stdio. FILEHANDLE may be an expression
whose value gives the name of the filehandle. Returns 1 upon success, 0
otherwise.
write or a print without a filehandle
will default to this FILEHANDLE. Second, references to variables
related to output will refer to this output channel. For example, if
you have to set the top of form format for more than one output channel,
you might do the following:
select(REPORT1); $^ = 'report1_top'; select(REPORT2); $^ = 'report2_top';FILEHANDLE may be an expression whose value gives the name of the actual filehandle. Thus:
$oldfh = select(STDERR); $| = 1; select($oldfh);
select) may be set explicitly
by assigning the name of the format to the `$~' variable.
Top of form processing is handled automatically: if there is
insufficient room on the current page for the formatted record, the page
is advanced by writing a form feed, a special top-of-page format is used
to format the new page header, and then the record is written. By
default the top-of-page format is the name of the filehandle with
_TOP appended, but it may be dynamically set to the format of
your choice by assigning the name to the `$^' variable while the
filehandle is selected. The number of lines remaining on the
current page is in variable `$-', which can be set to 0 to force a
new page.
If FILEHANDLE is unspecified, output goes to the current default
output channel, which starts out as `STDOUT' but may be changed by
the select operator. If the FILEHANDLE is an EXPR,
then the expression is evaluated and the resulting string is used to
look up the name of the FILEHANDLE at run time. See section Formats,
for more info.
Note that write is NOT the opposite of read.
open(tty, '/dev/tty');
<tty> =~ /^y/i && do foo(); # do foo if desired
if (/Version: *([0-9.]*)/) { $version = $1; }
next if m#^/usr/spool/uucp#;
# poor man's grep
$arg = shift;
while (<>) {
print if /$arg/o; # compile only once
}
if (($F1, $F2, $Etc) = ($foo =~ /^(\S+)\s+(\S+)\s*(.*)/))
This last example splits `$foo' into the first two words and the
remainder of the line, and assigns those three fields to `$F1',
`$F2' and `$Etc'. The conditional is true if any variables
were assigned, i.e. if the pattern matched.
The `g' modifier specifies global pattern matching--that is,
matching as many times as possible within the string. How it behaves
depends on the context. In an array context, it returns a list of
all the substrings matched by all the parentheses in the regular expression.
If there are no parentheses, it returns a list of all the matched strings,
as if there were parentheses around the whole pattern. In a scalar context,
it iterates through the string, returning TRUE each time it matches, and
FALSE when it eventually runs out of matches. (In other words, it remembers
where it left off last time and restarts the search at that point.) It
presumes that you have not modified the string since the last match.
Modifying the string between matches may result in undefined behavior.
(You can actually get away with in-place modifications via substr()
that do not change the length of the entire string. In general, however,
you should be using s///g for such modifications.) Examples:
# array context
($one,$five,$fifteen) = (`uptime` =~ /(\d+\.\d+)/g);
# scalar context
$/ = ""; $* = 1;
while ($paragraph = <>) {
while ($paragraph =~ /[a-z]['")]*[.!?]+['")]*\s/g) {
$sentences++;
}
}
print "$sentences\n";
/pattern/ search, except that it matches only
once between calls to the reset operator. This is a useful
optimization when you only want to see the first occurrence of something in
each file of a set of files, for instance. Only `??' patterns local
to the current package are reset.
s(foo)(bar) or s<foo>/bar/.
If no string is specified
via the `=~' or `!~' operator, the `$_' string is
searched and modified. (The string specified with `=~' must be a
scalar variable, an array element, or an assignment to one of those,
i.e. an lvalue.) If the pattern contains a `$' that looks like a
variable rather than an end-of-string test, the variable will be
interpolated into the pattern at run-time. If you only want the pattern
compiled once the first time the variable is interpolated, add an
`o' at the end. If the PATTERN evaluates to a null string,
the most recent successful regular expression is used instead.
See section Regular Expressions, for more info. Examples:
s/\bgreen\b/mauve/g; # don't change wintergreen
$path =~ s|/usr/bin|/usr/local/bin|;
s/Login: $foo/Login: $bar/; # run-time pattern
($foo = $bar) =~ s/bar/foo/;
$_ = 'abc123xyz';
s/\d+/$&*2/e; # yields `abc246xyz'
s/\d+/sprintf("%5d",$&)/e; # yields `abc 246xyz'
s/\w/$& x 2/eg; # yields `aabbcc 224466xxyyzz'
s/([^ ]*) *([^ ]*)/$2 $1/; # reverse 1st two fields
(Note the use of `$' instead of `\' in the last example.
See section Regular Expressions.)
while (<>) {
study;
print ".IX foo\n" if /\bfoo\b/;
print ".IX bar\n" if /\bbar\b/;
print ".IX blurfl\n" if /\bblurfl\b/;
...
print;
}
In searching for `/\bfoo\b/', only those locations in `$_'
that contain `f' will be looked at, because `f' is rarer than
`o'. In general, this is a big win except in pathological cases.
The only question is whether it saves you more time than it took to
build the linked list in the first place.
Note that if you have to look for strings that you don't know till
runtime, you can build an entire loop as a string and eval that to avoid
recompiling all your patterns all the time. Together with undefining
`$/' to input entire files as one record, this can be very fast,
often faster than specialized programs like `fgrep'. The following
scans a list of files (`@files') for a list of words
(`@words'), and prints out the names of those files that contain a
match:
$search = 'while (<>) { study;';
foreach $word (@words) {
$search .= "++\$seen{\$ARGV} if /\\b$word\\b/;\n";
}
$search .= "}";
@ARGV = @files;
undef $/
eval $search; # this screams
$/ = "\n"; # put back to normal input delim
foreach $file (sort keys(%seen)) {
print $file, "\n";
}
sed devotees, y is provided as a synonym for
tr. If the SEARCHLIST is delimited by bracketing quotes,
the REPLACEMENTLIST has its own pair of quotes, which may or may
not be bracketing quotes, e.g. tr[A-Z][a-z] or
tr(+-*/)/ABCD/.
If the `c' modifier is specified, the SEARCHLIST character
set is complemented. If the `d' modifier is specified, any
characters specified by SEARCHLIST that are not found in
REPLACEMENTLIST are deleted. (Note that this is slightly more
flexible than the behavior of some tr programs, which delete
anything they find in the SEARCHLIST, period.) If the `s'
modifier is specified, sequences of characters that were translated to
the same character are squashed down to 1 instance of the
character.
If the `d' modifier was used, the REPLACEMENTLIST is always
interpreted exactly as specified. Otherwise, if the
REPLACEMENTLIST is shorter than the SEARCHLIST, the final
character is replicated till it is long enough. If the
REPLACEMENTLIST is null, the SEARCHLIST is replicated. The
latter is useful for counting characters in a class, or for squashing
character sequences in a class.
Examples:
$ARGV[1] =~ y/A-Z/a-z/; # canonicalize to lower case
$cnt = tr/*/*/; # count the stars in $_
$cnt = tr/0-9//; # count the digits in $_
tr/a-zA-Z//s; # bookkeeper -> bokeper
($HOST = $host) =~ tr/a-z/A-Z/;
y/\001-@[-_{-\177/ /; # change non-alphas to space
# (before the c & s modifiers)
y/a-zA-Z/ /cs; # change non-alphas to single space
# (version 3.0 patchlevel 40+)
tr/\200-\377/\0-\177/; # delete 8th bit
alarm(15) will cause a `SIGALRM' at some point more than 14
seconds in the future. Only one timer may be counting at once. Each
call disables the previous timer, and an argument of 0 may be supplied
to cancel the previous timer without starting a new one. The returned
value is the amount of time remaining on the previous timer.
chroot to `$_'.
eval, prints the value of LIST to
`STDERR' and exits with the current value of `$!' (errno). As
of version 3.0 patchlevel 27, die without LIST specified is
equivalent todie 'Died';If `$!' is 0, exits with the value of `($? >> 8)' (`command` status). If `($? >> 8)' is 0, exits with 255. Inside an
eval, the error message is stuffed into `$@' and the
eval is terminated with the undefined value.
Equivalent examples:
die "Can't cd to spool: $!\n" unless chdir '/usr/spool/news'; chdir '/usr/spool/news' || die "Can't cd to spool: $!\n"If the value of EXPR does not end in a newline, the current script line number and input line number (if any) are also printed, and a newline is supplied. Hint: sometimes appending ", stopped" to your message will cause it to make better sense when the string "at foo line 123" is appended. Suppose you are running script "canasta".
die "/etc/games is no good"; die "/etc/games is no good, stopped";produce, respectively
/etc/games is no good at canasta line 123. /etc/games is no good, stopped at canasta line 123.See also
exit.
execvp() with the arguments
in LIST. If there is only one scalar argument, the argument is
checked for shell metacharacters. If there are any, the entire argument
is passed to `/bin/sh -c' for parsing. If there are none, the
argument is split into words and passed directly to execvp(),
which is more efficient. Note: exec (and system) do not
flush your output buffer, so you may need to set `$|' to avoid lost
output. Examples:
exec '/bin/echo', 'Your arguments are: ', @ARGV; exec "sort $outfile | uniq";If you don't really want to execute the first argument, but want to lie to the program you are executing about its own name, you can specify the program you actually want to run by assigning that to a variable and putting the name of the variable in front of the LIST without a comma. (This always forces interpretation of the LIST as a multi-valued list, even if there is only a single scalar in the list.) Example:
$shell = '/bin/csh'; exec $shell '-sh'; # pretend it's a login shell
$ans = <STDIN>; exit 0 if $ans =~ /^[Xx]/;See also
die. If EXPR is omitted, exits with 0 status.
fork() call. Returns the child pid to the parent process
and 0 to the child process. Note: unflushed buffers remain unflushed in
both processes, which means you may need to set `$|' to avoid
duplicate output.
($name,$passwd,$uid,$gid, $quota,$comment,$gcos,$dir,$shell) = getpw... ($name,$passwd,$gid,$members) = getgr... ($name,$aliases,$addrtype,$length,@addrs) = gethost... ($name,$aliases,$addrtype,$net) = getnet... ($name,$aliases,$proto) = getproto... ($name,$aliases,$port,$proto) = getserv...(If the entry doesn't exist you get a null list.) Within a scalar context, you get the name, unless the function was a lookup by name, in which case you get the other thing, whatever it is. (If the entry doesn't exist you get the undefined value.) For example:
$uid = getpwnam $name = getpwuid $name = getpwent $gid = getgrnam $name = getgrgid $name = getgrent etc.The `$members' value returned by
getgr... is a space
separated list of the login names of the members of the group.
For the gethost... functions, if the h_errno variable
is supported in C, it will be returned to you via `$?' if the function
call fails.
The `@addrs' value returned by a successful call
is a list of the raw addresses returned by the corresponding system
library call. In the Internet domain, each address is four bytes long and
you can unpack it by saying something like:
($a,$b,$c,$d) = unpack('C4',$addr[0]);
getpwuid.
$login = getlogin || (getpwuid($<))[0] || "Somebody";
getpgrp(2). If PID is omitted, returns process
group of current process. PID can be an expression.
getpriority(2) man page.) Will produce a fatal error if
used on a machine that doesn't implement getpriority(2).
ioctl(2) function.
You'll probably have to say
require "ioctl.ph"; # probably `/usr/local/lib/perl/ioctl.ph'first to get the correct function definitions. If `ioctl.ph' doesn't exist or doesn't have the correct definitions you'll have to roll your own, based on your C header files such as `<sys/ioctl.h>'. (There is a perl script called
h2ph
that comes with the perl kit which may help you in this.) SCALAR
will be read and/or written depending on the FUNCTION---a pointer
to the string value of SCALAR will be passed as the third argument
of the actual ioctl call. (If SCALAR has no string value
but does have a numeric value, that value will be passed rather than a
pointer to the string value. To guarantee this to be true, add a 0 to
the scalar before using it.) The pack() and unpack()
functions are useful for manipulating the values of structures used by
ioctl().
The following example sets the erase character to DEL.
require 'ioctl.ph';
$sgttyb_t = "ccccs"; # 4 chars and a short
if (ioctl(STDIN,$TIOCGETP,$sgttyb)) {
@ary = unpack($sgttyb_t,$sgttyb);
$ary[2] = 127;
$sgttyb = pack($sgttyb_t,@ary);
ioctl(STDIN,$TIOCSETP,$sgttyb)
|| die "Can't ioctl: $!";
}
The return value of ioctl (and fcntl) is as follows:
if OS returns: perl returns: -1 undefined value 0 string "0 but true" anything else that numberThus perl returns true on success and false on failure, yet you can still easily determine the actual value returned by the operating system:
($retval = ioctl(...)) || ($retval = -1); printf "System returned %d\n", $retval;
$cnt = kill 1, $child1, $child2; kill 9, @goners;If the signal is negative, kills process groups instead of processes. (On System V, a negative process number will also kill process groups, but that's not portable.) You may use a signal name in quotes.
setpgrp(2).
setpriority(2) man page.) Will produce a fatal error if
used on a machine that doesn't implement setpriority(2).
alarm() and sleep() calls, since sleep() is often
implemented using alarm().
require 'syscall.ph'; # may need to run h2ph syscall(&SYS_write, fileno(STDOUT), "hi there\n", 9);
read(2). It bypasses stdio, so mixing this with other kinds of
reads may cause confusion. Returns the number of bytes actually read,
or undef if there was an error. SCALAR will be grown or
shrunk to the length actually read. An OFFSET may be specified to
place the read data at some other place than the beginning of the
string.
write(2). It bypasses stdio, so mixing this with prints may
cause confusion. Returns the number of bytes actually written, or
undef if there was an error. An OFFSET may be specified
to place the read data at some other place than the beginning of the
string.
wait() call. To get the actual exit value divide
by 256. See also exec.
($user,$system,$cuser,$csystem) = times;
require "sys/wait.ph"; ... waitpid(-1,&WNOHANG);then you can do a non-blocking wait for any process. Non-blocking wait is only available on machines supporting either the
waitpid(2) or
wait4(2) system calls. However, waiting for a particular pid
with FLAGS of 0 is implemented everywhere. (Perl emulates
the system call by remembering the status values of processes that have
exited but have not been harvested by the Perl script yet.)
die, but doesn't
exit.
accept system call does. Returns true
if it succeeded, false otherwise. See section Interprocess Communication, for
an example.
bind system call does. Returns true
if it succeeded, false otherwise. NAME should be a packed address
of the proper type for the socket. See section Interprocess Communication, for
an example.
connect system call does. Returns true
if it succeeded, false otherwise. NAME should be a packed address of
the proper type for the socket. See section Interprocess Communication, for an
example.
# An internet sockaddr $sockaddr = 'S n a4 x8'; $hersockaddr = getpeername(S); ($family, $port, $heraddr) = unpack($sockaddr,$hersockaddr);
# An internet sockaddr $sockaddr = 'S n a4 x8'; $mysockaddr = getsockname(S); ($family, $port, $myaddr) = unpack($sockaddr,$mysockaddr);
listen system call does. Returns true
if it succeeded, false otherwise. See section Interprocess Communication, for an
example.
undef if you don't want
to pass an argument.
h2ph on `sys/socket.h' to get the proper values handy in
a perl library file. Return true if successful. See section Interprocess Communication, for an example.
msgctl. If CMD is
&IPC_STAT, then ARG must be a variable which will hold the
returned msqid_ds structure. Returns like ioctl: the
undefined value for error, "0 but true" for zero, or the actual return
value otherwise.
msgget. Returns the message
queue id, or the undefined value if there is an error.
msgsnd to send the message
MSG to the message queue ID. MSG must begin with the
long integer message type, which may be created with
`pack("L", $type)'. Returns true if successful, or false if
there is an error.
msgrcv to receive a message
from message queue ID into variable VAR with a maximum
message size of SIZE. Note that if a message is received, the
message type will be the first thing in VAR, and the maximum
length of VAR is SIZE plus the size of the message type.
Returns true if successful, or false if there is an error.
semctl. If CMD is
&IPC_STAT or &GETALL, then ARG must be a variable which will hold
the returned semid_ds structure or semaphore value array. Returns like
ioctl: the undefined value for error, "0 but true" for zero,
or the actual return value otherwise.
semget. Returns the semaphore
id, or the undefined value if there is an error.
semop to perform semaphore operations
such as signaling and waiting. OPSTRING must be a packed array of
semop structures. Each semop structure can be generated with
`pack("sss", $semnum, $semop, $semflag)'. The number of semaphore
operations is implied by the length of OPSTRING. Returns true if
successful, or false if there is an error. As an example, the
following code waits on semaphore $semnum of semaphore id $semid:
$semop = pack("sss", $semnum, -1, 0);
die "Semaphore trouble: $!\n" unless semop($semid, $semop);
To signal the semaphore, replace `-1' with `1'.
shmctl. If CMD is
&IPC_STAT, then ARG must be a variable which will hold the
returned shmid_ds structure. Returns like ioctl: the
undefined value for error, "0 but true" for zero, or the actual return
value otherwise.
shmget. Returns the shared
memory segment id, or the undefined value if there is an error.
time function to a 9-element
array with the time analyzed for the Greenwich timezone. Typically used
as follows:
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)
= gmtime(time);
All array elements are numeric, and come straight out of a `struct tm'.
In particular this means that $mon has the range `0..11' and
$wday has the range `0..6'. If EXPR is omitted, does
`gmtime(time)'.
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst)
= localtime(time);
All array elements are numeric, and come straight out of a `struct tm'.
In particular this means that $mon has the range `0..11' and $wday has
the range `0..6'. If EXPR is omitted, does
localtime(time).
gmtime() and localtime().
dbmopen in your program. If your system has neither dbm nor ndbm,
calling dbmopen produces a fatal error.
Values assigned to the associative array prior to the dbmopen are
lost. A certain number of values from the dbm file are cached in memory.
By default this number is 64, but you can increase it by preallocating
that number of garbage entries in the associative array before the
dbmopen. You can flush the cache if necessary with the reset
command.
If you don't have write access to the dbm file, you can only read
associative array variables, not set them. If you want to test whether
you can write, either use file tests or try setting a dummy array entry
inside an eval, which will trap the error.
Note that functions such as keys() and values() may return
huge array values when used on large dbm files. You may prefer to use
the each() function to iterate over large dbm files. Example:
# print out history file offsets
dbmopen(HIST,'/usr/lib/news/history',0666);
while (($key,$val) = each %HIST) {
print $key, ' = ', unpack('L',$val), "\n";
}
dbmclose(HIST);
sed
scripts. Use it at your own risk. Better yet, don't use it at all.
last command is like the break statement in C (as used
in loops); it immediately exits the loop in question. If the LABEL
is omitted, the command refers to the innermost enclosing loop. The
continue block, if any, is not executed:
line: while (<STDIN>) {
last line if /^$/; # exit when done with header
...
}
next command is like the continue statement in C; it
starts the next iteration of the loop:
line: while (<STDIN>) {
next line if /^#/; # discard comments
...
}
Note that if there were a continue block on the above, it would
get executed even on discarded lines. If the LABEL is omitted,
the command refers to the innermost enclosing loop.
redo command restarts the loop block without evaluating the
conditional again. The continue block, if any, is not executed.
If the LABEL is omitted, the command refers to the innermost
enclosing loop. This command is normally used by programs that want to
lie to themselves about what was just input:
# a simpleminded Pascal comment stripper
# (warning: assumes no { or } in strings)
line: while (<STDIN>) {
while (s|({.*}.*){.*}|$1 |) {}
s|{.*}| |;
if (s|{.*| |) {
$front = $_;
while (<STDIN>) {
if (/}/) { # end of comment?
s|^|$front{|;
redo line;
}
}
}
print;
}
sub require {
local($filename) = @_;
return 1 if $INC{$filename};
local($realfilename,$result);
ITER: {
foreach $prefix (@INC) {
$realfilename = "$prefix/$filename";
if (-f $realfilename) {
$result = do $realfilename;
last ITER;
}
}
die "Can't find $filename in \@INC";
}
die $@ if $@;
die "$filename did not return true value" unless $result;
$INC{$filename} = $realfilename;
$result;
}
Note that the file will not be included twice under the same specified
name. The file must return true as the last statement to indicate
successful execution of any initialization code, so it's customary to
end such a file with 1; unless you're sure it'll return true
otherwise.
do 'stat.pl';is just like
eval `cat stat.pl`;except that it's more efficient, more concise, keeps track of the current filename for error messages, and searches all the `-I' libraries if the file isn't in the current directory (see section Predefined Names, for more info). It's the same, however, in that it does reparse the file every time you call it, so if you are going to use the file inside a loop you might prefer to use `-P' and `#include', at the expense of a little more startup time. (The main problem with `#include' is that cpp doesn't grok `#' comments--a workaround is to use `;#' for standalone comments.) Note that the following are NOT equivalent:
do $foo; # eval a file do $foo(); # call a subroutineNote that inclusion of library routines is better done with the
require operator.
($package,$filename,$line) = caller;With EXPR, returns some extra information that the debugger uses to print a stack trace. The value of EXPR indicates how many call frames to go back before the current one.
sub declaration, and
returns the value of the last expression evaluated in SUBROUTINE.
If there is no subroutine by that name, produces a fatal error. (You
may use the defined operator to determine if a subroutine
exists.) If you pass arrays as part of LIST you may wish to pass
the length of the array in front of each array. (See section Subroutines.)
The parentheses are required to avoid confusion with the `do
EXPR' form.
SUBROUTINE may also be a single scalar variable, in which case the
name of the subroutine to execute is take from the variable.
As an alternate (and preferred) form, you may call a subroutine by
prefixing the name with an ampersand: `&foo(@args)'. If you
aren't passing any arguments, you don't have to use parentheses. If you
omit the parentheses, no `@_' array is passed to the subroutine.
The `&' form is also used to specify subroutines to the
defined and undef operators.
if (defined &$var) { &$var($parm); undef &$var; }
eval or do. All the listed elements must be
legal lvalues. This operator works by saving the current values of
those variables in LIST on a hidden stack and restoring them upon
exiting the block, subroutine or eval. This means that called
subroutines can also reference the local variable, but not the global
one. The LIST may be assigned to if desired, which allows you to
initialize your local variables. (If no initializer is given for a
particular variable, it is created with an undefined value.) Commonly
this is used to name the parameters to a subroutine. Examples:
sub RANGEVAL {
local($min, $max, $thunk) = @_;
local($result) = '';
local($i);
# Presumably $thunk makes reference to $i
for ($i = $min; $i < $max; $i++) {
$result .= eval $thunk;
}
$result;
}
if ($sw eq '-v') {
# init local array with global array
local(@ARGV) = @ARGV;
unshift(@ARGV,'echo');
system @ARGV;
}
# @ARGV restored
# temporarily add to digits associative array
if ($base12) {
# (NOTE: not claiming this is efficient!)
local(%digits) = (%digits,'t',10,'e',11);
do parse_num();
}
Note that local() is a run-time command, and so gets executed
every time through a loop, using up more stack storage each time until
it's all released at once when the loop is exited.
return is a bit slower.)
return wantarray ? () : undef;
print if defined $switch{'D'};
print "$val\n" while defined($val = pop(@ary));
die "Can't readlink $sym: $!"
unless defined($value = readlink $sym);
eval '@foo = ()' if defined(@foo);
die "No XYZ package defined" unless defined %_XYZ;
sub foo { defined &$bar ? &$bar(@_) : die "No bar"; }
See also undef.
continue block at the end of a loop to clear
variables and reset `??' searches so that they work again. The
expression is interpreted as a list of single characters (hyphens allowed
for ranges). All variables and arrays beginning with one of those letters
are reset to their pristine state. If the expression is omitted,
one-match searches (`?pattern?') are reset to match again. Only resets
variables or searches in the current package. Always returns 1.
Examples:
reset 'X'; # reset all X variables reset 'a-z'; # reset lower case variables reset; # just reset `??' searchesNote: resetting `A-Z' is not recommended since you'll wipe out your `ARGV' and `ENV' arrays. The use of reset on dbm associative arrays does not change the dbm file. (It does, however, flush any entries cached by perl, which may be useful if you are sharing the dbm file. Then again, maybe not.)
undef will probably not do what you expect on most predefined
variables or dbm array values.) Always returns the undefined value.
You can omit the EXPR, in which case nothing is undefined, but you
still get an undefined value that you could, for instance, return from a
subroutine. Examples:
undef $foo;
undef $bar{'blurfl'};
undef @ary;
undef %assoc;
undef &mysub;
return (wantarray ? () : undef) if $they_blew_it;
goto
suffers). Think of it as a goto with an intervening core dump and
reincarnation. If LABEL is omitted, restarts the program from the
top. WARNING: any files opened at the time of the dump will
NOT be open any more when the program is reincarnated, with
possible resulting confusion on the part of perl. See also
`-u'.
Example:
#!/usr/bin/perl
require 'getopt.pl';
require 'stat.pl';
%days = (
'Sun',1,
'Mon',2,
'Tue',3,
'Wed',4,
'Thu',5,
'Fri',6,
'Sat',7);
dump QUICKSTART if $ARGV[0] eq '-d';
QUICKSTART:
do Getopt('f');
...
die statement is executed, an
undefined value is returned by eval, and `$@' is set to the
error message. If there was no error, `$@' is guaranteed to be a
null string. If EXPR is omitted, evaluates `$_'. The final
semicolon, if any, may be omitted from the expression.
Note that, since eval traps otherwise-fatal errors, it is useful
for determining whether a particular feature (such as dbmopen or
symlink) is implemented. If is also Perl's exception
trapping mechanism, where the die operator is used to raise
exceptions.
If the code to be executed doesn't vary, you may use the eval
BLOCK form to trap run-time errors without incurring the penalty
of recompiling each time. The error, if any, is still returned in
`$@'. Evaluating a single-quoted string (as EXPR) has the
same effect, except that the eval EXPR form reports syntax
errors at run time via `$@', whereas the eval BLOCK
form reports syntax errors at compile time. The eval EXPR
form is optimized to eval BLOCK the first time it succeeds.
(Since the replacement side of a substitution is considered a
single-quoted string when you use the `e' modifier, the same
optimization occurs there.) Examples:
# make divide-by-zero non-fatal
eval { $answer = $a / $b; }; warn $@ if $@;
# optimized to same thing after first use
eval '$answer = $a / $b'; warn $@ if $@;
# a compile-time error
eval { $answer = };
# a run-time error
eval '$answer ='; # sets $@
q
operator is a generalized single quote, and the qq operator a
generalized double quote. The qx operator is a generalized
backquote. Any non-alphanumeric delimiter can be used in place of
`/', including newline. If the delimiter is an opening bracket or
parenthesis, the final delimiter will be the corresponding closing
bracket or parenthesis. (Embedded occurrences of the closing bracket
need to be backslashed as usual.) Examples:
$foo = q!I said, "You said, 'She said it.'"!;
$bar = q('This is it.');
$today = qx{ date };
$_ .= qq
*** The previous line contains the naughty word "$&".\n
if /(ibm|apple|awk)/; # :-)
srand().
rand operator. If EXPR
is omitted, does srand(time).
printf conventions. The
`*' character is not supported.
vec() can also be manipulated with the
logical operators `|', `&' and `^', which will assume a
bit vector operation is desired when both operands are strings. This
interpretation is not enabled unless there is at least one vec()
in your program, to protect older programs.
To transform a bit vector into a string or array of 0's and 1's, use
these:
$bits = unpack("b*", $vector);
@bits = split(//, unpack("b*", $vector));
If you know the exact length in bits, it can be used in place of the *.
Perl operators have the following associativity and precedence:
nonassoc print printf exec system sort reverse
chmod chown kill unlink utime die return
left ,
right = += \-= *= etc.
right ?:
nonassoc ..
left ||
left &&
left | ^
left &
nonassoc == != <=> eq ne cmp
nonassoc < > <= >= lt gt le ge
nonassoc chdir exit eval reset sleep rand umask
nonassoc -r -w -x etc.
left << >>
left + - .
left * / % x
left =~ !~
right ! ~ and unary minus
right **
nonassoc ++ --
left `('
As mentioned earlier, if any list operator (print, etc.) or any unary
operator (chdir, etc.) is followed by a left parenthesis as the next
token on the same line, the operator and arguments within parentheses
are taken to be of highest precedence, just like a normal function call.
Examples:
chdir $foo || die; # (chdir $foo) || die chdir($foo) || die; # (chdir $foo) || die chdir ($foo) || die; # (chdir $foo) || die chdir +($foo) || die; # (chdir $foo) || die
but, because `*' is higher precedence than `||':
chdir $foo * 20; # chdir ($foo * 20) chdir($foo) * 20; # (chdir $foo) * 20 chdir ($foo) * 20; # (chdir $foo) * 20 chdir +($foo) * 20; # chdir ($foo * 20) rand 10 * 20; # rand (10 * 20) rand(10) * 20; # (rand 10) * 20 rand (10) * 20; # (rand 10) * 20 rand +(10) * 20; # rand (10 * 20)
In the absence of parentheses, the precedence of list operators such as
print, sort or chmod is either very high or very
low depending on whether you look at the left side of operator or the
right side of it. For example, in
@ary = (1, 3, sort 4, 2); print @ary; # prints 1324
the commas on the right of the sort are evaluated before the sort, but the commas on the left are evaluated after. In other words, list operators tend to gobble up all the arguments that follow them, and then act like a simple term with regard to the preceding expression. Note that you have to be careful with parens:
# These evaluate exit before doing the print: print($foo, exit); # Obviously not what you want. print $foo, exit; # Nor is this. # These do the print before evaluating exit: (print $foo), exit; # This is what you want. print($foo), exit; # Or this. print ($foo), exit; # Or even this.
Also note that
print ($foo & 255) + 1, "\n";
probably doesn't do what you expect at first glance.
A subroutine may be declared as follows:
sub NAME BLOCK
Any arguments passed to the routine come in as array `@_', that is
`($_[0], $_[1], ...)'. The array `@_' is a local array,
but its values are references to the actual scalar parameters. The
return value of the subroutine is the value of the last expression
evaluated, and can be either an array value or a scalar value.
Alternately, a return statement may be used to specify the returned
value and exit the subroutine. To create local variables see the
local operator.
A subroutine is called using the do operator or the &
operator.
Example:
sub MAX {
local($max) = pop(@_);
foreach $foo (@_) {
$max = $foo if $max < $foo;
}
$max;
}
...
$bestday = &MAX($mon,$tue,$wed,$thu,$fri);
# get a line, combining continuation lines
# that start with whitespace
sub get_line {
$thisline = $lookahead;
line: while ($lookahead = <STDIN>) {
if ($lookahead =~ /^[ \t]/) {
$thisline .= $lookahead;
}
else {
last line;
}
}
$thisline;
}
$lookahead = <STDIN>; # get first line
while ($_ = do get_line()) {
...
}
Use array assignment to a local list to name your formal arguments:
sub maybeset {
local($key, $value) = @_;
$foo{$key} = $value unless $foo{$key};
}
This also has the effect of turning call-by-reference into call-by-value, since the assignment copies the values.
Subroutines may be called recursively. If a subroutine is called using the `&' form, the argument list is optional. If omitted, no `@_' array is set up for the subroutine; the `@_' array at the time of the call is visible to subroutine instead.
do foo(1,2,3); # pass three arguments &foo(1,2,3); # the same do foo(); # pass a null list &foo(); # the same &foo; # pass no arguments--more efficient
Sometimes you don't want to pass the value of an array to a subroutine
but rather the name of it, so that the subroutine can modify the global
copy of it rather than working with a local copy. In perl you can refer
to all the objects of a particular name by prefixing the name with a
star: `*foo'. When evaluated, it produces a scalar value that
represents all the objects of that name, including any filehandle,
format or subroutine. When assigned to within a local()
operation, it causes the name mentioned to refer to whatever `*'
value was assigned to it. Example:
sub doubleary {
local(*someary) = @_;
foreach $elem (@someary) {
$elem *= 2;
}
}
do doubleary(*foo);
do doubleary(*bar);
Assignment to `*name' is currently recommended only inside a
local(). You can actually assign to `*name' anywhere, but
the previous referent of `*name' may be stranded forever. This may
or may not bother you.
Note that scalars are already passed by reference, so you can modify
scalar arguments without using this mechanism by referring explicitly to
the `$_[nnn]' in question. You can modify all the elements of an
array by passing all the elements as scalars, but you have to use the
`*' mechanism to push, pop or change the size of an
array. The `*' mechanism will probably be more efficient in any
case.
Since a `*name' value contains unprintable binary data, if it is
used as an argument in a print, or as a `%s' argument in a
printf or sprintf, it then has the value `*name',
just so it prints out pretty.
Even if you don't want to modify an array, this mechanism is useful for passing multiple arrays in a single LIST, since normally the LIST mechanism will merge all the array values so that you can't extract out the individual arrays.
The patterns used in pattern matching are regular expressions such as those supplied in the Version 8 regexp routines. (In fact, the routines are derived from Henry Spencer's freely redistributable reimplementation of the V8 routines.) In addition, `\w' matches an alphanumeric character (including `_') and `\W' a nonalphanumeric. Word boundaries may be matched by `\b', and non-boundaries by `\B'. A whitespace character is matched by `\s', non-whitespace by `\S'. A numeric character is matched by `\d', non-numeric by `\D'. You may use `\w', `\s' and `\d' within character classes. Also, `\n', `\r', `\f', `\t' and `\NNN' have their normal interpretations. Within character classes `\b' represents backspace rather than a word boundary. Alternatives may be separated by `|'. The bracketing construct `(...)' may also be used, in which case `\<digit>' matches the digit'th substring. (Outside of the pattern, always use `$' instead of `\' in front of the digit. The scope of `$<digit>' (and `$`', `$&' and `$'') extends to the end of the enclosing BLOCK or eval string, or to the next pattern match with subexpressions. The `\<digit>' notation sometimes works outside the current pattern, but should not be relied upon.) You may have as many parentheses as you wish. If you have more than 9 substrings, the variables `$10', `$11', ... refer to the corresponding substring. Within the pattern, `\10', `\11', etc. refer back to substrings if there have been at least that many left parens before the backreference. Otherwise (for backward compatibilty) `\10' is the same as `\010', a backspace, and `\11' the same as `\011', a tab. And so on. (`\1' through `\9' are always backreferences.)
`$+' returns whatever the last bracket match matched. `$&' returns the entire matched string. (`$0' used to return the same thing, but not any more.) `$`' returns everything before the matched string. `$'' returns everything after the matched string. Examples:
s/^([^ ]*) *([^ ]*)/$2 $1/; # swap first two words
if (/Time: (..):(..):(..)/) {
$hours = $1;
$minutes = $2;
$seconds = $3;
}
By default, the `^' character is only guaranteed to match at the beginning of the string, the `$' character only at the end (or before the newline at the end) and perl does certain optimizations with the assumption that the string contains only one line. The behavior of `^' and `$' on embedded newlines will be inconsistent. You may, however, wish to treat a string as a multi-line buffer, such that the `^' will match after any newline within the string, and `$' will match before any newline. At the cost of a little more overhead, you can do this by setting the variable `$*' to 1. Setting it back to 0 makes perl revert to its old behavior.
To facilitate multi-line substitutions, the `.' character never matches a newline (even when `$*' is 0). In particular, the following leaves a newline on the `$_' string:
$_ = <STDIN>; s/.*(some_string).*/$1/;
If the newline is unwanted, try one of
s/.*(some_string).*\n/$1/; s/.*(some_string)[^\000]*/$1/; s/.*(some_string)(.|\n)*/$1/; chop; s/.*(some_string).*/$1/; /(some_string)/ && ($_ = $1);
Any item of a regular expression may be followed with digits in curly brackets of the form `{n,m}', where n gives the minimum number of times to match the item and m gives the maximum. The form `{n}' is equivalent to `{n,n}' and matches exactly n times. The form `{n,}' matches n or more times. (If a curly bracket occurs in any other context, it is treated as a regular character.) The `*' modifier is equivalent to `{0,}', the `+' modifier to `{1,}' and the `?' modifier to `{0,1}'. There is no limit to the size of n or m, but large numbers will chew up more memory.
You will note that all backslashed metacharacters in perl are alphanumeric, such as `\b', `\w', `\n'. Unlike some other regular expression languages, there are no backslashed symbols that aren't alphanumeric. So anything that looks like `\\', `\(', `\)', `\<', `\>', `\{', or `\}' is always interpreted as a literal character, not a metacharacter. This makes it simple to quote a string that you want to use for a pattern but that you are afraid might contain metacharacters. Simply quote all the non-alphanumeric characters:
$pattern =~ s/(\W)/\\$1/g;
Output record formats for use with the write operator may
declared as follows:
format NAME = FORMLIST .
If name is omitted, format `STDOUT' is defined. FORMLIST consists of a sequence of lines, each of which may be of one of three types:
Picture lines are printed exactly as they look, except for certain fields that substitute values into the line. Each picture field starts with either `@' or `^'. The `@' field (not to be confused with the array marker `@') is the normal case; `^' fields are used to do rudimentary multi-line text block filling. The length of the field is supplied by padding out the field with multiple `<', `>', or `|' characters to specify, respectively, left justification, right justification, or centering. As an alternate form of right justification, you may also use `#' characters (with an optional `.') to specify a numeric field. (Use of `^' instead of `@' causes the field to be blanked if undefined.) If any of the values supplied for these fields contains a newline, only the text up to the newline is printed. The special field `@*' can be used for printing multi-line values. It should appear by itself on a line.
The values are specified on the following line, in the same order as the picture fields. The values should be separated by commas.
Picture fields that begin with `^' rather than `@' are treated specially. The value supplied must be a scalar variable name which contains a text string. Perl puts as much text as it can into the field, and then chops off the front of the string so that the next time the variable is referenced, more of the text can be printed. Normally you would use a sequence of fields in a vertical stack to print out a block of text. If you like, you can end the final field with `...', which will appear in the output if the text was too long to appear in its entirety. You can change which characters are legal to break on by changing the variable `$:' to a list of the desired characters.
Since use of `^' fields can produce variable length records if the text to be formatted is short, you can suppress blank lines by putting the tilde (`~') character anywhere in the line. (Normally you should put it in the front if possible, for visibility.) The tilde will be translated to a space upon output. If you put a second tilde contiguous to the first, the line will be repeated until all the fields on the line are exhausted. (If you use a field of the `@' variety, the expression you supply had better not give the same value every time forever!)
# a report on the /etc/passwd file
format STDOUT_TOP =
Passwd File
Name Login Office Uid Gid Home
------------------------------------------------------------------
.
format STDOUT =
@<<<<<<<<<<<<<<<<<< @||||||| @<<<<<<@>>>> @>>>> @<<<<<<<<<<<<<<<<<
$name, $login, $office,$uid,$gid, $home
.
# a report from a bug report form
format STDOUT_TOP =
Bug Reports
@<<<<<<<<<<<<<<<<<<<<<<< @||| @>>>>>>>>>>>>>>>>>>>>>>>
$system, $%, $date
------------------------------------------------------------------
.
format STDOUT =
Subject: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$subject
Index: @<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$index, $description
Priority: @<<<<<<<<<< Date: @<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$priority, $date, $description
From: @<<<<<<<<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$from, $description
Assigned to: @<<<<<<<<<<<<<<<<<<<<<< ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$programmer, $description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<<<<<<
$description
~ ^<<<<<<<<<<<<<<<<<<<<<<<...
$description
.
It is possible to intermix prints with writes on the same output
channel, but you'll have to handle `$-' (lines left on the page)
yourself.
If you are printing lots of fields that are usually blank, you should consider using the reset operator between records. Not only is it more efficient, but it can prevent the bug of adding another field and forgetting to zero it.
The IPC facilities of perl are built on the Berkeley socket mechanism. If you don't have sockets, you can ignore this section. The calls have the same names as the corresponding system calls, but the arguments tend to differ, for two reasons. First, perl file handles work differently than C file descriptors. Second, perl already knows the length of its strings, so you don't need to pass that information. Here is a sample client (untested):
($them,$port) = @ARGV;
$port = 2345 unless $port;
$them = 'localhost' unless $them;
$SIG{'INT'} = 'dokill';
sub dokill { kill 9,$child if $child; }
require 'sys/socket.ph';
$sockaddr = 'S n a4 x8';
chop($hostname = `hostname`);
($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
unless $port =~ /^\d+$/;
($name, $aliases, $type, $len, $thisaddr) =
gethostbyname($hostname);
($name, $aliases, $type, $len, $thataddr) = gethostbyname($them);
$this = pack($sockaddr, &AF_INET, 0, $thisaddr);
$that = pack($sockaddr, &AF_INET, $port, $thataddr);
socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
connect(S, $that) || die "connect: $!";
select(S); $| = 1; select(stdout);
if ($child = fork) {
while (<>) {
print S;
}
sleep 3;
do dokill();
}
else {
while (<S>) {
print;
}
}
($port) = @ARGV;
$port = 2345 unless $port;
require 'sys/socket.ph';
$sockaddr = 'S n a4 x8';
($name, $aliases, $proto) = getprotobyname('tcp');
($name, $aliases, $port) = getservbyname($port, 'tcp')
unless $port =~ /^\d+$/;
$this = pack($sockaddr, &AF_INET, $port, "\0\0\0\0");
select(NS); $| = 1; select(stdout);
socket(S, &PF_INET, &SOCK_STREAM, $proto) || die "socket: $!";
bind(S, $this) || die "bind: $!";
listen(S, 5) || die "connect: $!";
select(S); $| = 1; select(stdout);
for (;;) {
print "Listening again\n";
($addr = accept(NS,S)) || die $!;
print "accept ok\n";
($af,$port,$inetaddr) = unpack($sockaddr,$addr);
@inetaddr = unpack('C4',$inetaddr);
print "$af $port @inetaddr\n";
while (<NS>) {
print;
print NS;
}
}
The following names have special meaning to perl. I could have used alphabetic symbols for some of these, but I didn't want to take the chance that someone would say `reset "a-zA-Z"' and wipe them all out. You'll just have to suffer along with these silly symbols. Most of them have reasonable mnemonics, or analogues in one of the shells.
while (<>) {... # only equivalent in while!
while ($_ = <>) {...
/^Subject:/
$_ =~ /^Subject:/
y/a-z/A-Z/
$_ =~ y/a-z/A-Z/
chop
chop($_)
(Mnemonic: underline is understood in certain operations.)
eof). (Mnemonic: many programs use `.' to mean the current
line number.)
awk's
RS variable, including treating blank lines as delimiters if set to the
null string. You may set it to a multicharacter string to match a
multi-character delimiter.
Note that setting it to "\n\n" means something slightly different
than setting it to "", if the file contains consecutive blank
lines. Setting it to "" will treat two or more consecutive blank
lines as a single blank line.
Setting it to "\en\en" will blindly assume that the next input character
belongs to the next paragraph, even if it's a newline.
(Mnemonic: `/' is used to delimit line
boundaries when quoting poetry.)
print operator. Ordinarily the
print operator simply prints out the comma separated fields you
specify. In order to get behavior more like awk, set this variable
as you would set awk's OFS variable to specify what is printed
between fields. (Mnemonic: what is printed when there is a `,' in
your print statement.)
print operator. Ordinarily the
print operator simply prints out the comma separated fields you specify,
with no trailing newline or record separator assumed. In order to get
behavior more like awk, set this variable as you would set
awk's ORS variable to specify what is printed at the end of the
print. (Mnemonic: you set `$\' instead of adding `\n' at the
end of the print. Also, it's just like `/', but it's what you get
"back" from perl.)
awk's OFMT variable. There are times,
however, when awk and perl have differing notions of what
is in fact numeric. Also, the initial value is `%.20g' rather than
`%.6g', so you need to set `$#' explicitly to get awk's
value. (Mnemonic: `#' is the number sign.)
_TOP
appended. (Mnemonic: points to top of page.)
write or print
on the currently selected output channel. Default is 0. Note that
`STDOUT' will typically be line buffered if output is to the terminal
and block buffered otherwise. Setting this variable is useful primarily
when you are outputting to a pipe, such as when you are running a
perl script under rsh and want to see the output as it's happening.
(Mnemonic: when you want your pipes to be piping hot.)
system operator. Note that this is the status word returned by
the wait() system call, so the exit value of the subprocess is
actually `($? >> 8)'. `$? & 255' gives which signal, if any,
the process died from, and whether there was a core dump. (Mnemonic:
similar to sh and ksh.)
eval enclosed by the current BLOCK).
(Mnemonic: like `&' in some editors.)
eval enclosed by
the current BLOCK). (Mnemonic: ` often precedes a quoted
string.)
eval enclosed by
the current BLOCK). (Mnemonic: ' often follows a quoted string.)
Example:
$_ = 'abcdefghi'; /def/; print "$`:$&:$'\n"; # prints abc:def:ghi
/Version: (.*)|Revision: (.*)/ && ($rev = $+);(Mnemonic: be positive and forward looking.)
ps(1) program sees. (Mnemonic: same as sh and
ksh.)
awk (or Fortran) when subscripting
and when evaluating the index() and substr() functions.
(Mnemonic: `[' begins subscripts.)
# see if getc is available
($version,$patchlevel) =
$] =~ /(\d+\.\d+).*\nPatch level: (\d+)/;
print STDERR "(No filename completion available.)\n"
if $version * 1000 + $patchlevel < 2016;
or, used numerically,
warn "No checksumming!\n" if $] < 3.019;(Mnemonic: Is this version of perl in the right bracket?)
$foo{$a,$b,$c}
it really means
$foo{join($;, $a, $b, $c)}
But don't put
@foo{$a,$b,$c} # a slice--note the @
which means
($foo{$a},$foo{$b},$foo{$c})
Default is `\034', the same as SUBSEP in awk. Note that if
your keys contain binary data there might not be any safe value for
`$;'. (Mnemonic: comma (the syntactic subscript separator) is a
semi-semicolon. Yeah, I know, it's pretty lame, but `$,' is
already taken for something more important.)
die operator. (Mnemonic: What just went bang?)
eval command. If null,
the last eval parsed and executed correctly (although the
operations you invoked may have failed in the normal fashion). (Mnemonic:
Where was the syntax error "at"?)
$< = $>; # set real uid to the effective uid ($<,$>) = ($>,$<); # swap real and effective uid(Mnemonic: it's the uid you went TO, if you're running setuid.) Note: `$<' and `$>' can only be swapped on machines supporting
setreuid().
getgid(), and the subsequent ones by getgroups(), one of
which may be the same as the first number. (Mnemonic: parentheses are
used to GROUP things. The real gid is the group you
LEFT, if you're running setgid.)
getegid(), and the subsequent ones by getgroups(), one of
which may be the same as the first number. (Mnemonic: parentheses are
used to GROUP things. The effective gid is the group that's
RIGHT for you, if you're running setgid.)
Note: `$<', `$>', `$(' and `$)' can only be set on
machines that support the corresponding set[re][ug]id() routine.
`$(' and `$)' can only be swapped on machines supporting
setregid().
undef to
disable inplace editing. (Mnemonic: value of `-i' switch.)
do EXPR command or the
require command. It initially consists of the arguments to any
`-I' command line switches, followed by the default perl
library, probably `/usr/local/lib/perl', followed by `.', to
represent the current directory.
do or require. The key is the
filename you specified, and the value is the location of the file
actually found. The require command uses this array to determine
whether a given file has already been included.
sub handler { # 1st argument is signal name
local($sig) = @_;
print "Caught a SIG$sig--shutting down\n";
close(LOG);
exit(0);
}
$SIG{'INT'} = 'handler';
$SIG{'QUIT'} = 'handler';
...
$SIG{'INT'} = 'DEFAULT'; # restore default action
$SIG{'QUIT'} = 'IGNORE'; # ignore SIGQUIT
The `SIG' array only contains values for the signals actually set
within the perl script.
Perl provides a mechanism for alternate namespaces to protect packages
from stomping on each others variables. By default, a perl script
starts compiling into the package known as `main'. By use of the
package declaration, you can switch namespaces. The scope of the
package declaration is from the declaration itself to the end of the
enclosing block (the same scope as the local() operator).
Typically it would be the first declaration in a file to be included by
the require operator. You can switch into a package in more than
one place; it merely influences which symbol table is used by the
compiler for the rest of that block. You can refer to variables and
filehandles in other packages by prefixing the identifier with the
package name and a single quote. If the package name is null, the
`main' package as assumed.
Only identifiers starting with letters are stored in the packages symbol table. All other symbols are kept in package `main'. In addition, the identifiers `STDIN', `STDOUT', `STDERR', `ARGV', `ARGVOUT', `ENV', `INC' and `SIG' are forced to be in package `main', even when used for other purposes than their built-in one. Note also that, if you have a package called `m', `s' or `y', the you can't use the qualified form of an identifier since it will be interpreted instead as a pattern match, a substitution or a translation.
eval'ed strings are compiled in the package in which the
eval was compiled in. (Assignments to `$SIG{}', however,
assume the signal handler specified is in the `main' package.
Qualify the signal handler name if you wish to have a signal handler in a
package.) For an example, examine `perldb.pl' in the perl library.
It initially switches to the `DB' package so that the debugger
doesn't interfere with variables in the script you are trying to debug.
At various points, however, it temporarily switches back to the `main'
package to evaluate various expressions in the context of the `main'
package.
The symbol table for a package happens to be stored in the associative array of that name prepended with an underscore. The value in each entry of the associative array is what you are referring to when you use the `*name' notation. In fact, the following have the same effect (in package `main', anyway), though the first is more efficient because it does the symbol table lookups at compile time:
local(*foo) = *bar;
local($_main{'foo'}) = $_main{'bar'};
You can use this to print out all the variables in a package, for instance. Here is `dumpvar.pl' from the perl library:
package dumpvar;
sub main'dumpvar {
($package) = @_;
local(*stab) = eval("*_$package");
while (($key,$val) = each(%stab)) {
{
local(*entry) = $val;
if (defined $entry) {
print "\$$key = '$entry'\n";
}
if (defined @entry) {
print "\@$key = (\n";
foreach $num ($[ .. $#entry) {
print " $num\t'",$entry[$num],"'\n";
}
print ")\n";
}
if ($key ne "_$package" && defined %entry) {
print "\%$key = (\n";
foreach $key (sort keys(%entry)) {
print " $key\t'",$entry{$key},"'\n";
}
print ")\n";
}
}
}
}
Note that, even though the subroutine is compiled in package `dumpvar', the name of the subroutine is qualified so that its name is inserted into package `main'.
Each programmer will, of course, have his or her own preferences in regards to formatting, but there are some general guidelines that will make your programs easier to read.
open(FOO,$foo) || die "Can't open $foo: $!";is better than
die "Can't open $foo: $!" unless open(FOO,$foo);because the second way hides the main point of the statement in a modifier. On the other hand
print "Starting analysis\n" if $verbose;is better than
$verbose && print "Starting analysis\n";since the main point isn't whether the user typed `-v' or not. Similarly, just because an operator lets you assume default arguments doesn't mean that you have to make use of the defaults. The defaults are there for lazy systems programmers writing one-shot programs. If you want your program to be readable, consider supplying the argument. Along the same lines, just because you can omit parentheses in many places doesn't mean that you ought to:
return print reverse sort num values array; return print(reverse(sort num (values(%array))));When in doubt, parenthesize. At the very least it will let some poor schmuck bounce on the % key in vi. Even if you aren't in doubt, consider the mental welfare of the person who has to maintain the code after you, and who will probably put parens in the wrong place.
last operator so you can exit in the
middle. Just outdent it a little to make it more visible:
line:
for (;;) {
statements;
last line if $foo;
next line if /^#/;
statements;
}
eval to see if it fails. If you
know what version or patchlevel a particular feature was implemented, you
can test `$]' to see if it will be there.
If you invoke perl with a `-d' switch, your script will be run under a debugging monitor. It will halt before the first executable statement and ask you for a command, such as:
print DB'OUT expr. The `DB'OUT' filehandle is opened
to `/dev/tty', regardless of where `STDOUT' may be redirected
to.If you want to modify the debugger, copy `perldb.pl' from the perl library to your current directory and modify it as necessary. (You'll also have to put `-I.' on your command line.) You can do some customization by setting up a `.perldb' file which contains initialization code. For instance, you could make aliases like these:
$DB'alias{'len'} = 's/^len(.*)/p length($1)/';
$DB'alias{'stop'} = 's/^stop (at|in)/b/';
$DB'alias{'.'} =
's/^\./p "\$DB\'sub(\$DB\'line):\t",\$DB\'line[\$DB\'line]/';
Perl is designed to make it easy to write secure setuid and setgid scripts. Unlike shells, which are based on multiple substitution passes on each line of the script, perl uses a more conventional evaluation scheme with fewer hidden "gotchas". Additionally, since the language has more built-in functionality, it has to rely less upon external (and possibly untrustworthy) programs to accomplish its purposes.
In an unpatched 4.2 or 4.3bsd kernel, setuid scripts are intrinsically insecure, but this kernel feature can be disabled. If it is, perl can emulate the setuid and setgid mechanism when it notices the otherwise useless setuid/gid bits on perl scripts. If the kernel feature isn't disabled, perl will complain loudly that your setuid script is insecure. You'll need to either disable the kernel setuid script feature, or put a C wrapper around the script.
When perl is executing a setuid script, it takes special precautions to prevent you from falling into any obvious traps. (In some ways, a perl script is more secure than the corresponding C program.) Any command line argument, environment variable, or input is marked as tainted, and may not be used, directly or indirectly, in any command that invokes a subshell, or in any command that modifies files, directories or processes. Any variable that is set within an expression that has previously referenced a tainted value also becomes tainted (even if it is logically impossible for the tainted value to influence the variable). For example:
$foo = shift; # $foo is tainted
$bar = $foo,'bar'; # $bar is also tainted
$xxx = <>; # Tainted
$path = $ENV{'PATH'}; # Tainted, but see below
$abc = 'abc'; # Not tainted
system "echo $foo"; # Insecure
system "/bin/echo", $foo; # Secure (doesn't use sh)
system "echo $bar"; # Insecure
system "echo $abc"; # Insecure until PATH set
$ENV{'PATH'} = '/bin:/usr/bin';
$ENV{'IFS'} = '' if $ENV{'IFS'} ne '';
$path = $ENV{'PATH'}; # Not tainted
system "echo $abc"; # Is secure now!
open(FOO,"$foo"); # OK
open(FOO,">$foo"); # Not OK
open(FOO,"echo $foo|"); # Not OK, but...
open(FOO,"-|") || exec 'echo', $foo; # OK
$zzz = `echo $foo`; # Insecure, zzz tainted
unlink $abc,$foo; # Insecure
umask $foo; # Insecure
exec "echo $foo"; # Insecure
exec "echo", $foo; # Secure (doesn't use sh)
exec "sh", '-c', $foo; # Considered secure, alas
The taintedness is associated with each scalar value, so some elements of an array can be tainted, and others not.
If you try to do something insecure, you will get a fatal error saying
something like "Insecure dependency" or "Insecure PATH". Note that you
can still write an insecure system call or exec, but only by
explicitly doing something like the last example above. You can also
bypass the tainting mechanism by referencing subpatterns---perl
presumes that if you reference a substring using `$1', `$2', etc,
you knew what you were doing when you wrote the pattern:
$ARGV[0] =~ /^-P(\w+)$/; $printer = $1; # Not tainted
This is fairly secure since `\w+' doesn't match shell metacharacters. Use of `.+' would have been insecure, but perl doesn't check for that, so you must be careful with your patterns. This is the ONLY mechanism for untainting user supplied filenames if you want to do file operations on them (unless you make `$>' equal to `$<').
It's also possible to get into trouble with other operations that don't care whether they use tainted values. Make judicious use of the file tests in dealing with any user-supplied filenames. When possible, do opens and such after setting `$> = $<'. Perl doesn't prevent you from opening tainted filenames for reading, so be careful what you print out. The tainting mechanism is intended to prevent stupid mistakes, not to remove the need for thought.
chdir has no argument.
chdir has no argument and `HOME' is not set.
require 'perldb.pl'
Apart from these, perl uses no other environment variables, except to make them available to the script being executed, and to child processes. However, scripts running setuid would do well to execute the following lines before doing anything else, just to keep people honest:
$ENV{'PATH'} = '/bin:/usr/bin'; # or whatever you need
$ENV{'SHELL'} = '/bin/sh' if $ENV{'SHELL'} ne '';
$ENV{'IFS'} = '' if $ENV{'IFS'} ne '';
The only file that perl creates, other than user specified files, is:
/tmp/perl-eXXXXXX temporary file for `-e' commands.
A2p takes an awk script specified on the command line (or
from standard input) and produces a comparable perl script on the
standard output.
Options include:
awk script is always invoked with this
`-F' switch.
awk script that
processes the password file, you might say:
a2p -7 -nlogin.password.uid.gid.gcos.shell.homeAny delimiter can be used to separate the field names.
A2p cannot do as good a job translating as a human would, but it usually does pretty well. There are some areas where you may want to examine the perl script produced and tweak it some. Here are some of them, in no particular order.
There is an awk idiom of putting int() around a string
expression to force numeric interpretation, even though the argument is
always integer anyway. This is generally unneeded in perl, but
a2p can't tell if the argument is always going to be integer, so
it leaves it in. You may wish to remove it.
Perl differentiates numeric comparison from string comparison.
Awk has one operator for both that decides at run time which
comparison to do. A2p does not try to do a complete job of
awk emulation at this point. Instead it guesses which one you
want. It's almost always right, but it can be spoofed. All such
guesses are marked with the comment `#???'. You should go through
and check them. You might want to run at least once with the `-w'
switch to perl, which will warn you if you use `==' where
you should have used eq.
Perl does not attempt to emulate the behavior of awk in which
nonexistent array elements spring into existence simply by being
referenced. If somehow you are relying on this mechanism to create null
entries for a subsequent for...in, they won't be there in perl.
If a2p makes a split line that assigns to a list of variables that looks like `(Fld1, Fld2, Fld3...)' you may want to rerun a2p using the `-n' option mentioned above. This will let you name the fields throughout the script. If it splits to an array instead, the script is probably referring to the number of fields somewhere.
The exit statement in awk doesn't necessarily exit; it
goes to the END block if there is one. Awk scripts that do
contortions within the END block to bypass the block under such
circumstances can be simplified by removing the conditional in the END
block and just exiting directly from the perl script.
Perl has two kinds of arrays, numerically-indexed and associative.
Awk arrays are usually translated to associative arrays, but if
you happen to know that the index is always going to be numeric you
could change the `{...}' to `[...]'. Iteration over
an associative array is done using the keys() function, but
iteration over a numeric array is NOT. You might need to modify any
loop that is iterating over the array in question.
Awk starts by assuming OFMT has the value `%.6g'. Perl
starts by assuming its equivalent, `$#', to have the value
`%.20g'. You'll want to set `$#' explicitly if you use the
default value of OFMT.
Near the top of the line loop will be the split operation that is
implicit in the awk script. There are times when you can move
this down past some conditionals that test the entire record so that the
split is not done as often.
For aesthetic reasons you may wish to change the array base `$['
from 1 back to perl's default of 0, but remember to change all array
subscripts AND all substr() and index() operations to
match.
Cute comments that say "# Here is a workaround because awk is dumb" are passed through unmodified.
Awk scripts are often embedded in a shell script that pipes stuff
into and out of awk. Often the shell script wrapper can be
incorporated into the perl script, since perl can start up pipes into
and out of itself, and can do other things that awk can't do by
itself.
Scripts that refer to the special variables RSTART and RLENGTH can often be simplified by referring to the variables `$`', `$&' and `$'', as long as they are within the scope of the pattern match that sets them.
The produced perl script may have subroutines defined to deal with awk's
semantics regarding getline and print. Since a2p
usually picks correctness over efficiency. it is almost always possible
to rewrite such code to be more efficient by discarding the semantic
sugar.
For efficiency, you may wish to remove the keyword from any return statement that is the last statement executed in a subroutine. A2p catches the most common case, but doesn't analyze embedded blocks for subtler cases.
`ARGV[0]' translates to `$ARGV0', but `ARGV[n]' translates to `$ARGV[$n]'. A loop that tries to iterate over `ARGV[0]' won't find it.
A2p uses no environment variables.
It would be possible to emulate awk's behavior in selecting string versus numeric operations at run time by inspection of the operands, but it would be gross and inefficient. Besides, a2p almost always guesses right.
Storage for the awk syntax tree is currently static, and can run
out.
S2p takes a sed script specified on the command line (or
from standard input) and produces a comparable perl script on the
standard output.
Options include:
sed script was always invoked with a
`sed -n'. Otherwise a switch parser is prepended to the front of
the script.
sed script was never invoked with a `sed -n'.
Otherwise a switch parser is prepended to the front of the script.
The perl script produced looks very sed-ish, and there may very
well be better ways to express what you want to do in perl. For
instance, s2p does not make any use of the split operator,
but you might want to.
The perl script you end up with may be either faster or slower than the
original sed script. If you're only interested in speed you'll
just have to try it both ways. Of course, if you want to do something
sed doesn't do, you have no choice.
S2p uses no environment variables.
h2ph converts any C header files specified to the corresponding Perl header file format. It is most easily run while in `/usr/include':
cd /usr/include; h2ph * sys/*
C header files are located in the `/usr/include' directory and end with the extension `.h'. Perl header files are typically located in `/usr/local/lib/perl', with the extension `.ph' to distinguish the files from a C header file.
No environment variables are used. The only warnings you will probably see from h2ph are the usual warnings if it can't read or write the files involved.
evals so that you can get at the definitions
that it can translate.
Compilation errors will tell you the line number of the error, with an indication of the next token or token type that was to be examined. (In the case of a script passed to perl via `-e' switches, each `-e' is counted as one line.)
Setuid scripts have additional constraints that can produce error messages such as "Insecure dependency". See section Setuid Scripts.
This chapter points out traps and pitfalls you may run into if you are
used to awk, C, sed or shell programming.
Accustomed awk users should take special note of the
following:
ifs and whiles.substr() and index().split operator has different
arguments.print statement does not add field and record separators unless
you set `$,' and `$\'.next, exit and continue work differently.Awk Perl ARGC $#ARGV ARGV[0] $0 FILENAME $ARGV FNR $. - something FS (whatever you like) NF $#Fld, or some such NR $. OFMT $# OFS $, ORS $\ RLENGTH length($&) RS $/ RSTART length($`) SUBSEP $;
awk construct through a2p and see what
it gives you (see section a2p - Awk to Perl Translator for more info).Cerebral C programmers should take note of the following:
ifs and whiles.
elsif rather than else if
break and continue become last and next,
respectively.switch statement.
printf does not implement `*'.
link, unlink, rename, etc. return
nonzero for success, not zero (0).
Seasoned sed programmers should take note of the following:
Sharp shell programmers should take note of the following:
csh.csh) do several levels of substitution on each
command line. Perl does substitution only in certain constructs
such as double quotes, backticks, angle brackets and search
patterns.
Perl is at the mercy of your machine's definitions of various
operations such as type casting, atof() and sprintf().
If your stdio requires a seek or eof between reads and writes
on a particular stream, so does perl. (This doesn't apply to
sysread() and syswrite().)
While none of the built-in data types have any arbitrary size limits (apart from memory size), there are still a few arbitrary limits: a given identifier may not be longer than 255 characters, and no component of your `PATH' may be longer than 255 if you use `-S'. A regular expression may not compile to more than 32767 bytes internally.
Perl actually stands for Pathologically Eclectic Rubbish Lister, but don't tell anyone I said that.
Perl was designed and implemented by...
...Larry Wall <lwall@netlabs.com>
MS-DOS port of perl by...
...Diomidis Spinellis <dds@cc.ic.ac.uk>
Texinfo version of perl manual by...
...Jeff Kellem <composer@Beyond.Dreams.ORG>
The Perl book, Programming Perl, has the following omissions and goofs.
eval '/usr/bin/perlshould read
eval 'exec /usr/bin/perl
sum program only works for
very small files. To do larger files, use
undef $/;
$checksum = unpack("%32C*",<>) % 32767;
alarm and sleep refer to signal
`SIGALARM'. These should refer to `SIGALRM'.
qx// construct is now a synonym for backticks.
ps(1).s///ee caused multiple
evaluations of the replacement expression. This is to be construed as a
feature.(LIST) x $count now does array replication.
FILEHANDLE_TOP rather than top.
eval {} and sort {} constructs were added in
version 4.018.
pack and unpack were added in 4.019.
THIS SECTION IS CURRENTLY INCOMPLETE and may change without notice!!
(As may the rest of this document... ;-)
/PATTERN/io
?PATTERN?
accept(NEWSOCKET,GENERICSOCKET)
atan2(X,Y)
bind(SOCKET,NAME)
binmode(FILEHANDLE)
binmode FILEHANDLE
chdir(EXPR)
chdir EXPR
chdir
chmod(LIST)
chmod LIST
chop(LIST)
chop(VARIABLE)
chop VARIABLE
chop
chown(LIST)
chown LIST
chroot(FILENAME)
chroot FILENAME
chroot
close(FILEHANDLE)
close FILEHANDLE
closedir(DIRHANDLE)
closedir DIRHANDLE
connect(SOCKET,NAME)
cos(EXPR)
cos EXPR
cos
crypt(PLAINTEXT,SALT)
dbmclose(ASSOC_ARRAY)
dbmclose ASSOC_ARRAY
dbmopen(ASSOC,DBNAME,MODE)
defined(EXPR)
defined EXPR
delete $ASSOC{KEY}
die(LIST)
die LIST
die
do BLOCK
do EXPR
do SUBROUTINE (LIST)
dump LABEL
dump
each(ASSOC_ARRAY)
each ASSOC_ARRAY
endpwent
endgrent
endhostent
endnetent
endprotoent
endpwent
endservent
eof(FILEHANDLE)
eof()
eof
eval(EXPR)
eval EXPR
eval
exec(LIST)
exec LIST
exit(EXPR)
exit EXPR
exp(EXPR)
exp EXPR
exp
fcntl(FILEHANDLE,FUNCTION,SCALAR)
fileno(FILEHANDLE)
fileno FILEHANDLE
flock(FILEHANDLE,OPERATION)
fork
getc(FILEHANDLE)
getc FILEHANDLE
getc
getgrent
getgrgid(GID)
getgrnam(NAME)
gethostbyaddr(ADDR,ADDRTYPE)
gethostbyname(NAME)
gethostent
getlogin
getnetbyaddr(ADDR,ADDRTYPE)
getnetbyname(NAME)
getnetent
getpeername(SOCKET)
getpgrp(PID)
getpgrp PID
getpgrp
getppid
getpriority(WHICH,WHO)
getprotobyname(NAME)
getprotobynumber(NUMBER)
getprotoent
getpwent
getpwnam(NAME)
getpwuid(UID)
getservbyname(NAME,PROTO)
getservbyport(PORT,PROTO)
getservent
getsockname(SOCKET)
getsockopt(SOCKET,LEVEL,OPTNAME)
gmtime(EXPR)
gmtime EXPR
gmtime
goto LABEL
grep(EXPR,LIST)
hex(EXPR)
hex EXPR
hex
index(STR,SUBSTR)
int(EXPR)
int EXPR
int
ioctl(FILEHANDLE,FUNCTION,SCALAR)
join(EXPR,LIST)
join(EXPR,ARRAY)
keys(ASSOC_ARRAY)
keys ASSOC_ARRAY
kill(LIST)
kill LIST
last LABEL
last
length(EXPR)
length EXPR
length
link(OLDFILE,NEWFILE)
listen(SOCKET,QUEUESIZE)
local(LIST)
localtime(EXPR)
localtime EXPR
localtime
log(EXPR)
log EXPR
log
lstat(FILEHANDLE)
lstat FILEHANDLE
lstat(EXPR)
lstat SCALARVARIABLE
m/PATTERN/io
/PATTERN/io
mkdir(FILENAME,MODE)
next LABEL
next
oct(EXPR)
oct EXPR
oct
open(FILEHANDLE,EXPR)
open(FILEHANDLE)
open FILEHANDLE
opendir(DIRHANDLE,EXPR)
ord(EXPR)
ord EXPR
ord
pack(TEMPLATE,LIST)
pipe(READHANDLE,WRITEHANDLE)
pop(ARRAY)
pop ARRAY
print(FILEHANDLE LIST)
print(LIST)
print FILEHANDLE LIST
print LIST
print
printf(FILEHANDLE LIST)
printf(LIST)
printf FILEHANDLE LIST
printf LIST
printf
push(ARRAY,LIST)
q/STRING/
qq/STRING/
rand(EXPR)
rand EXPR
rand
read(FILEHANDLE,SCALAR,LENGTH)
readdir(DIRHANDLE)
readdir DIRHANDLE
readlink(EXPR)
readlink EXPR
readlink
recv(SOCKET,SCALAR,LEN,FLAGS)
redo LABEL
redo
rename(OLDNAME,NEWNAME)
require(EXPR)
require EXPR
require
reset(EXPR)
reset EXPR
reset
return LIST
reverse(LIST)
reverse LIST
rewinddir(DIRHANDLE)
rewinddir DIRHANDLE
rindex(STR,SUBSTR)
rmdir(FILENAME)
rmdir FILENAME
rmdir
s/PATTERN/REPLACEMENT/gieo
seek(FILEHANDLE,POSITION,WHENCE)
seekdir(DIRHANDLE,POS)
select(FILEHANDLE)
select
select(RBITS,WBITS,EBITS,TIMEOUT)
send(SOCKET,MSG,FLAGS,TO)
send(SOCKET,MSG,FLAGS)
setgrent
sethostent(STAYOPEN)
setnetent(STAYOPEN)
setpgrp(PID,PGRP)
setpriority(WHICH,WHO,PRIORITY)
setprotoent(STAYOPEN)
setpwent
setservent(STAYOPEN)
setsockopt(SOCKET,LEVEL,OPTNAME,OPTVAL)
shift(ARRAY)
shift ARRAY
shift
shutdown(SOCKET,HOW)
sin(EXPR)
sin EXPR
sin
sleep(EXPR)
sleep EXPR
sleep
socket(SOCKET,DOMAIN,TYPE,PROTOCOL)
socketpair(SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL)
sort(SUBROUTINE LIST)
sort(LIST)
sort SUBROUTINE LIST
sort LIST
splice(ARRAY,OFFSET,LENGTH,LIST)
splice(ARRAY,OFFSET,LENGTH)
splice(ARRAY,OFFSET)
split(/PATTERN/,EXPR,LIMIT)
split(/PATTERN/,EXPR)
split(/PATTERN/)
split
sprintf(FORMAT,LIST)
sqrt(EXPR)
sqrt EXPR
sqrt
srand(EXPR)
srand EXPR
srand
stat(FILEHANDLE)
stat FILEHANDLE
stat(EXPR)
stat SCALARVARIABLE
study(SCALAR)
study SCALAR
study
substr(EXPR,OFFSET,LEN)
symlink(OLDFILE,NEWFILE)
syscall(LIST)
syscall LIST
system(LIST)
system LIST
tell(FILEHANDLE)
tell FILEHANDLE
tell
telldir(DIRHANDLE)
telldir DIRHANDLE
time
times
tr/SEARCHLIST/REPLACEMENTLIST/
umask(EXPR)
umask EXPR
umask
undef(EXPR)
undef EXPR
undef
unlink(LIST)
unlink LIST
unlink
unpack(TEMPLATE,EXPR)
unshift(ARRAY,LIST)
utime(LIST)
utime LIST
values(ASSOC_ARRAY)
values ASSOC_ARRAY
vec(EXPR,OFFSET,BITS)
wait
wantarray
warn(LIST)
warn LIST
write(FILEHANDLE)
write(EXPR)
write
y/SEARCHLIST/REPLACEMENTLIST/
accept function
alarm function
pop function
push function
reverse function
shift function
unshift function
delete function
each function
keys function
values function
bind function
binmode function
select system call
chdir function
symlink function exists
chgrp function (part of chown)
chmod example
chop example
chop function
chown example
chown function
chroot function
close function
close function example
closedir function
connect function
select
continue statement
cos function
crypt function
dbmclose
dbmopen
dbmclose function
dbmopen function
dbmclose function
dbmopen function
defined function
defined function examples
delete function
delete function example
chop)
die function
die function example
chdir
mkdir
opendir
readdir
rewinddir
rmdir
seekdir
telldir
do BLOCK
do EXPR
do EXPR example
do SUBROUTINE
dump function example
dump, creating a core file
each function example
each function, Associative arrays
else statement
elsif statement
ord with unpack
substr with unpack example
eof function
eof function example
eval function
unpack
die function
dump function
each function
eof function
exec function
execing a program in a script
exit function
flock function
getlogin function
join function
keys function
kill function
last function
localtime function
reset function
select system call
study function
symlink function
syscall function
select
symlink exists
chmod function
chop function
chown function
close function
delete function
do EXPR
ord with unpack
substr with unpack
gmtime function
grep function
ioctl function
getpeername function
join function
local function
next function
next function
oct function
q operator
qq operator
redo function
select(FILEHANDLE) function
sort function
splice function
split function
stat function
stat function and underscore
times function
tr/SEARCHLIST/REPLACEMENTLIST/
unpack function
each with dbm file
study and eval
unpack to emulate ord
unpack to emulate substr
wantarray function
y/SEARCHLIST/REPLACEMENTLIST/
defined function
open function
pack function
splice function
undef function
unlink function
s/PATTERN/REPLACEMENT/
exec function
exec function example
exec
exit function
exit function example
exp trigonometric function
fcntl function
fileno function
flock function
for statement
foreach statement
fork function
seek)
getc function
getlogin example
getlogin function
getpeername function
getpeername function example
getpgrp function
getppid function
getpriority function
getsockname function
getsockopt function
gmtime function
gmtime function example
goto function
goto LABEL
grep function
grep function example
hex function
undump
if modifier
if statement
index function
int function
ioctl function example
ioctl system call
getpeername function
bind function
connect function
getpeername function
listen system call
recv system call
join function
join function example
keys function example
keys function, Associative arrays
kill function
kill function example
last function
last function example
length function
link function
listen function
reverse function
local function
local function example
localtime function
localtime function example
log function (base e)
last function
next function
lstat function
exp
log function (base e)
sin function
sqrt function
mkdir function
next function
next function example
oct function example
open function
open function examples
opendir function
pack function
split function, join
unpack function
ord function
pack function
pack function examples
crypt function
pipe function
pipe system call
pop function
open
print function
printf function
push function
q operator example
qq operator example
rand function
read function
readdir function
readlink function
recv function
redo function
redo function example
rename function
rename system call
require function
require operator implementation
reset function
reset function example
?? searches
readdir
return function
reverse function
rewinddir function
rindex function
rmdir function
rindex)
s/PATTERN/REPLACEMENT/ examples
s/PATTERN/REPLACEMENT/ function
seek function
seekdir function
select system call
select system call example
select(FILEHANDLE) function
select(FILEHANDLE) function example
send function
setpgrp function
setpriority function
setsockopt function
shift function
shutdown function
die function
sin function
sin)
sleep function
socket function
socketpair function
listen system call
recv system call
sort function
sort function example
stat
study
splice function
splice function example
split function
split function example
sprintf function
sqrt function
srand function
stat function
stat function and underscore example
stat function example
index)
index function
rindex function
study function
study function example
substr function
symlink function
symlink function example
syscall function
syscall function example
system function
sum program implementation
tell function
telldir function
time function
alarm function
times function
times function example
tr/SEARCHLIST/REPLACEMENTLIST/
tr/SEARCHLIST/REPLACEMENTLIST/ example
exp function
umask function
undef function
undef function examples
stat function
unless modifier
unless statement
unlink function
unlink function examples
unpack function
unpack function example
unshift function
study and eval example
unpack to emulate ord
unpack to emulate substr example
utime function
values function
vec function
wait function
wantarray function
wantarray function example
warn function
while modifier
while statement
write function
y/SEARCHLIST/REPLACEMENTLIST/
y/SEARCHLIST/REPLACEMENTLIST/ example
(c) by Christopher Sima /
e-mail: sima@isis.wu-wien.ac.at