With methods 2 and 3, Perl starts parsing the input file from the beginning, unless you've specified a ``-x'' switch, in which case it scans for the first line starting with "#!" and containing the word ``perl'', and starts there instead. This is useful for running a program embedded in a larger message. (In this case you would indicate the end of the program using the "__END__" token.)
The "#!" line is always examined for switches as the line is being parsed. Thus, if you're on a machine that allows only one argument with the "#!" line, or worse, doesn't even recognize the "#!" line, you still can get consistent switch behaviour regardless of how Perl was invoked, even if ``-x'' was used to find the beginning of the program.
Because historically some operating systems silently chopped off kernel interpretation of the "#!" line after 32 characters, some switches may be passed in on the command line, and some may not; you could even get a ``-'' without its letter, if you're not careful. You probably want to make sure that all your switches fall either before or after that 32-character boundary. Most switches don't actually care if they're processed redundantly, but getting a ``-'' instead of a complete switch could cause Perl to try to execute standard input instead of your program. And a partial -I switch could also cause odd results.
Some switches do care if they are processed twice, for instance combinations of -l and -0. Either put all the switches after the 32-character boundary (if applicable), or replace the use of -0digits by "BEGIN{ $/ = "\0digits"; }".
Parsing of the "#!" switches starts wherever ``perl'' is mentioned in the line. The sequences ``-*'' and ``- '' are specifically ignored so that you could, if you were so inclined, say
#!/bin/sh
#! -*- perl -*- -p
eval 'exec perl -x -wS $0 ${1+"$@"}'
if 0;
to let Perl see the ``-p'' switch.
A similar trick involves the env program, if you have it.
#!/usr/bin/env perl
The examples above use a relative path to the perl interpreter, getting whatever version is first in the user's path. If you want a specific version of Perl, say, perl5.14.1, you should place that directly in the "#!" line's path.
If the "#!" line does not contain the word ``perl'' nor the word ``indir'', the program named after the "#!" is executed instead of the Perl interpreter. This is slightly bizarre, but it helps people on machines that don't do "#!", because they can tell a program that their SHELL is /usr/bin/perl, and Perl will then dispatch the program to the correct interpreter for them.
After locating your program, Perl compiles the entire program to an internal form. If there are any compilation errors, execution of the program is not attempted. (This is unlike the typical shell script, which might run part-way through before finding a syntax error.)
If the program is syntactically correct, it is executed. If the program runs off the end without hitting an exit() or die() operator, an implicit exit(0) is provided to indicate successful completion.
extproc perl -S -your_switches
as the first line in "*.cmd" file (``-S'' due to a bug in cmd.exe's `extproc' handling).
$ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
$ exit++ + ++$status != 0 and $exit = $status = undef;
at the top of your program, where -mysw are any command line switches you want to pass to Perl. You can now invoke the program directly, by saying "perl program", or as a DCL procedure, by saying @program (or implicitly via DCL$PATH by just using the name of the program).
This incantation is a bit much to remember, but Perl will display it for you if you say "perl "-V:startperl"".
Command-interpreters on non-Unix systems have rather different ideas on quoting than Unix shells. You'll need to learn the special characters in your command-interpreter ("*", "\" and """ are common) and how to protect whitespace and these characters to run one-liners (see -e below).
On some systems, you may have to change single-quotes to double ones, which you must not do on Unix or Plan 9 systems. You might also have to change a single % to a %%.
For example:
# Unix
perl -e 'print "Hello world\n"'
# MS-DOS, etc.
perl -e "print \"Hello world\n\""
# VMS
perl -e "print ""Hello world\n"""
The problem is that none of this is reliable: it depends on the command and it is entirely possible neither works. If 4DOS were the command shell, this would probably work better:
perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""
CMD.EXE in Windows NT slipped a lot of standard Unix functionality in when nobody was looking, but just try to find documentation for its quoting rules.
There is no general solution to all of this. It's just a mess.
In this documentation, "#!/usr/bin/perl" on the first line of the program will stand in for whatever method works on your system. You are advised to use a specific path if you care about a specific version.
#!/usr/local/bin/perl5.14
or if you just want to be running at least version, place a statement like this at the top of your program:
use 5.014;
#!/usr/bin/perl -spi.orig # same as -s -p -i.orig
A "--" signals the end of options and disables further option processing. Any arguments after the "--" are treated as filenames and arguments.
Switches include:
find . -name '*.orig' -print0 | perl -n0e unlink
The special value 00 will cause Perl to slurp files in paragraph mode. Any value 0400 or above will cause Perl to slurp files whole, but by convention the value 0777 is the one normally used for this purpose.
You can also specify the separator character using hexadecimal notation: -0xHHH..., where the "H" are valid hexadecimal digits. Unlike the octal form, this one may be used to specify any Unicode character, even those beyond 0xFF. So if you really want a record separator of 0777, specify it as -0x1FF. (This means that you cannot use the ``-x'' option with a directory name that consists of hexadecimal digits, or else Perl will think you have specified a hex number to -0.)
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F.
-a implicitly sets ``-n''.
As of 5.8.1, the -C can be followed either by a number or a list of option letters. The letters, their numeric values, and effects are as follows; listing the letters is equal to summing the numbers.
I 1 STDIN is assumed to be in UTF-8
O 2 STDOUT will be in UTF-8
E 4 STDERR will be in UTF-8
S 7 I + O + E
i 8 UTF-8 is the default PerlIO layer for input streams
o 16 UTF-8 is the default PerlIO layer for output streams
D 24 i + o
A 32 the @ARGV elements are expected to be strings encoded
in UTF-8
L 64 normally the "IOEioA" are unconditional, the L makes
them conditional on the locale environment variables
(the LC_ALL, LC_CTYPE, and LANG, in the order of
decreasing precedence) -- if the variables indicate
UTF-8, then the selected "IOEioA" are in effect
a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
code in debugging mode.
For example, -COE and -C6 will both turn on UTF-8-ness on both STDOUT and STDERR. Repeating letters is just redundant, not cumulative nor toggling.
The "io" options mean that any subsequent open() (or similar I/O operations) in main program scope will have the ":utf8" PerlIO layer implicitly applied to them, in other words, UTF-8 is expected from any input stream, and UTF-8 is produced to any output stream. This is just the default set via "${^OPEN}", with explicit layers in open() and with binmode() one can manipulate streams as usual. This has no effect on code run in modules.
-C on its own (not followed by any number or option list), or the empty string "" for the ``PERL_UNICODE'' environment variable, has the same effect as -CSDL. In other words, the standard I/O handles and the default "open()" layer are UTF-8-fied but only if the locale environment variables indicate a UTF-8 locale. This behaviour follows the implicit (and problematic) UTF-8 behaviour of Perl 5.8.0. (See ``UTF-8 no longer default under UTF-8 locales'' in perl581delta.)
You can use -C0 (or "0" for "PERL_UNICODE") to explicitly disable all the above Unicode features.
The read-only magic variable "${^UNICODE}" reflects the numeric value of this setting. This variable is set during Perl startup and is thereafter read-only. If you want runtime effects, use the three-arg open() (see ``open'' in perlfunc), the two-arg binmode() (see ``binmode'' in perlfunc), and the "open" pragma (see open).
(In Perls earlier than 5.8.1 the -C switch was a Win32-only switch that enabled the use of Unicode-aware ``wide system call'' Win32 APIs. This feature was practically unused, however, and the command line switch was therefore ``recycled''.)
Note: Since perl 5.10.1, if the -C option is used on the "#!" line, it must be specified on the command line as well, since the standard streams are already set up at this point in the execution of the perl interpreter. You can also use binmode() to set the encoding of an I/O stream.
For example, to watch how perl executes your program, use -Dtls. Another nice value is -Dx, which lists your compiled syntax tree, and -Dr displays compiled regular expressions; the format of the output is explained in perldebguts.
As an alternative, specify a number instead of list of letters (e.g., -D14 is equivalent to -Dtls):
1 p Tokenizing and parsing (with v, displays parse
stack)
2 s Stack snapshots (with v, displays all stacks)
4 l Context (loop) stack processing
8 t Trace execution
16 o Method and overloading resolution
32 c String/numeric conversions
64 P Print profiling info, source file input state
128 m Memory and SV allocation
256 f Format processing
512 r Regular expression parsing and execution
1024 x Syntax tree dump
2048 u Tainting checks
4096 U Unofficial, User hacking (reserved for private,
unreleased use)
16384 X Scratchpad allocation
32768 D Cleaning up
65536 S Op slab allocation
131072 T Tokenizing
262144 R Include reference counts of dumped variables
(eg when using -Ds)
524288 J show s,t,P-debug (don't Jump over) on opcodes within
package DB
1048576 v Verbose: use in conjunction with other flags to
increase the verbosity of the output. Is a no-op on
many of the other flags
2097152 C Copy On Write
4194304 A Consistency checks on internal structures
8388608 q quiet - currently only suppresses the "EXECUTING"
message
16777216 M trace smart match resolution
33554432 B dump suBroutine definitions, including special
Blocks like BEGIN
67108864 L trace Locale-related info; what gets output is very
subject to change
134217728 i trace PerlIO layer processing. Set PERLIO_DEBUG to
the filename to trace to.
268435456 y trace y///, tr/// compilation and execution
All these flags require -DDEBUGGING when you compile the Perl executable (but see ":opd" in Devel::Peek or ``'debug' mode'' in re which may change this). See the INSTALL file in the Perl source distribution for how to do this.
If you're just trying to get a print out of each line of Perl code as it executes, the way that "sh -x" provides for shell scripts, you can't use Perl's -D switch. Instead do this
# If you have "env" utility env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program # Bourne shell syntax $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program # csh syntax % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)
See perldebug for details and variations.
Perl can be built so that it by default will try to execute $Config{sitelib}/sitecustomize.pl at startup (in a BEGIN block). This is a hook that allows the sysadmin to customize how Perl behaves. It can for instance be used to add entries to the @INC array to make Perl find modules in non-standard locations.
Perl actually inserts the following code:
BEGIN {
do { local $!; -f "$Config{sitelib}/sitecustomize.pl"; }
&& do "$Config{sitelib}/sitecustomize.pl";
}
Since it is an actual "do" (not a "require"), sitecustomize.pl doesn't need to return a true value. The code is run in package "main", in its own lexical scope. However, if the script dies, $@ will not be set.
The value of $Config{sitelib} is also determined in C code and not read from "Config.pm", which is not loaded.
The code is executed very early. For example, any changes made to @INC will show up in the output of `perl -V`. Of course, "END" blocks will be likewise executed very late.
To determine at runtime if this capability has been compiled in your perl, you can check the value of $Config{usesitecustomize}.
-F implicitly sets both ``-a'' and ``-n''.
If no extension is supplied, and your system supports it, the original file is kept open without a name while the output is redirected to a new file with the original filename. When perl exits, cleanly or not, the original file is unlinked.
If the extension doesn't contain a "*", then it is appended to the end of the current filename as a suffix. If the extension does contain one or more "*" characters, then each "*" is replaced with the current filename. In Perl terms, you could think of this as:
($backup = $extension) =~ s/\*/$file_name/g;
This allows you to add a prefix to the backup file, instead of (or in addition to) a suffix:
$ perl -pi'orig_*' -e 's/bar/baz/' fileA # backup to
# 'orig_fileA'
Or even to place backup copies of the original files into another directory (provided the directory already exists):
$ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to
# 'old/fileA.orig'
These sets of one-liners are equivalent:
$ perl -pi -e 's/bar/baz/' fileA # overwrite current file $ perl -pi'*' -e 's/bar/baz/' fileA # overwrite current file $ perl -pi'.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig' $ perl -pi'*.orig' -e 's/bar/baz/' fileA # backup to 'fileA.orig'
From the shell, saying
$ perl -p -i.orig -e "s/foo/bar/; ... "
is the same as using the program:
#!/usr/bin/perl -pi.orig
s/foo/bar/;
which is equivalent to
#!/usr/bin/perl
$extension = '.orig';
LINE: while (<>) {
if ($ARGV ne $oldargv) {
if ($extension !~ /\*/) {
$backup = $ARGV . $extension;
}
else {
($backup = $extension) =~ s/\*/$ARGV/g;
}
rename($ARGV, $backup);
open(ARGVOUT, ">$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.
As shown above, Perl creates the backup file whether or not any output is actually changed. So this is just a fancy way to copy files:
$ perl -p -i'/some/file/path/*' -e 1 file1 file2 file3...
or
$ perl -p -i'.orig' -e 1 file1 file2 file3...
You can use "eof" without parentheses to locate the end of each input file, in case you want to append to each file, or reset line numbering (see example in ``eof'' in perlfunc).
If, for a given file, Perl is unable to create the backup file as specified in the extension then it will skip that file and continue on with the next one (if it exists).
For a discussion of issues surrounding file permissions and -i, see ``Why does Perl let me delete read-only files? Why does -i clobber protected files? Isn't this a bug in Perl?'' in perlfaq5.
You cannot use -i to create directories or to strip extensions from files.
Perl does not expand "~" in filenames, which is good, since some folks use it for their backup files:
$ perl -pi~ -e 's/foo/bar/' file1 file2 file3...
Note that because -i renames or deletes the original file before creating a new file of the same name, Unix-style soft and hard links will not be preserved.
Finally, the -i switch does not impede execution when no files are given on the command line. In this case, no backup is made (the original file cannot, of course, be determined) and processing proceeds from STDIN to STDOUT as might be expected.
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.
-Mmodule executes "use" module ";" before executing your program. This loads the module and calls its "import" method, causing the module to have its default effect, typically importing subroutines or giving effect to a pragma. You can use quotes to add extra code after the module name, e.g., '-MMODULE qw(foo bar)'.
If the first character after the -M or -m is a dash (-) then the 'use' is replaced with 'no'. This makes no difference for -m.
A little builtin syntactic sugar means you can also say -mMODULE=foo,bar or -MMODULE=foo,bar as a shortcut for '-MMODULE qw(foo bar)'. This avoids the need to use quotes when importing symbols. The actual code generated by -MMODULE=foo,bar is "use module split(/,/,q{foo,bar})". Note that the "=" form removes the distinction between -m and -M; that is, -mMODULE=foo,bar is the same as -MMODULE=foo,bar.
A consequence of the "split" formulation is that -MMODULE=number never does a version check, unless "MODULE::import()" itself is set up to do a version check, which could happen for example if MODULE inherits from Exporter.
LINE:
while (<>) {
... # your program goes here
}
Note that the lines are not printed by default. See ``-p'' to have lines printed. If a file named by an argument cannot be opened for some reason, Perl warns you about it and moves on to the next file.
Also note that "<>" passes command line arguments to ``open'' in perlfunc, which doesn't necessarily interpret them as file names. See perlop for possible security implications.
Here is an efficient way to delete all files that haven't been modified for at least a week:
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 (but it's not faster than using the -delete switch available in newer versions of find. It does suffer from the bug of mishandling newlines in pathnames, which you can fix if you follow the example under -0.
"BEGIN" and "END" blocks may be used to capture control before or after the implicit program loop, just as in awk.
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for some reason, Perl warns you about it, and moves on to the next file. Note that the lines are printed automatically. An error occurring during printing is treated as fatal. To suppress printing use the ``-n'' switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control before or after the implicit loop, just as in awk.
#!/usr/bin/perl -s
if ($xyz) { print "$xyz\n" }
Do note that a switch like --help creates the variable "${-help}", which is not compliant with "use strict "refs"". Also, when using this option on a script with warnings enabled you may get a lot of spurious ``used only once'' warnings.
On some platforms, this also makes Perl append suffixes to the filename while searching for it. For example, on Win32 platforms, the ``.bat'' and ``.cmd'' suffixes are appended if a lookup for the original name fails, and if the name does not already end in one of those suffixes. If your Perl was compiled with "DEBUGGING" turned on, using the -Dp switch to Perl shows how the search progresses.
Typically this is used to emulate "#!" startup on platforms that don't support "#!". It's also convenient when debugging a script that uses "#!", and is thus normally found by the shell's $PATH search mechanism.
This example works on many platforms that have a shell compatible with Bourne shell:
#!/usr/bin/perl
eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
if $running_under_some_shell;
The system ignores the first line and feeds the program to /bin/sh, which proceeds to try to execute the Perl program 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 program if necessary. After Perl locates the program, it parses the lines and ignores them because the variable $running_under_some_shell is never true. If the program will be interpreted by csh, you will need to replace "${1+"$@"}" with $*, even though that doesn't understand embedded spaces (and such) in the argument list. 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 perl -wS $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;
If the filename supplied contains directory separators (and so is an absolute or relative pathname), and if that file is not found, platforms that append file extensions will do so and try to look for the file with those extensions added, one by one.
On DOS-like platforms, if the program does not contain directory separators, it will first be searched for in the current directory before being searched for on the PATH. On Unix platforms, the program will be searched for strictly on the PATH.
Note: This is not a substitute for "-T"! This is meant to be used only as a temporary development aid while securing legacy code: for real production code and for new secure code written from scratch, always use the real ``-T''.
$ perl -V:libc
libc='/lib/libc-2.2.4.so';
$ perl -V:lib.
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
libc='/lib/libc-2.2.4.so';
$ perl -V:lib.*
libpth='/usr/local/lib /lib /usr/lib';
libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
lib_ext='.a';
libc='/lib/libc-2.2.4.so';
libperl='libperl.a';
....
Additionally, extra colons can be used to control formatting. A trailing colon suppresses the linefeed and terminator ``;'', allowing you to embed queries into shell commands. (mnemonic: PATH separator ``:''.)
$ echo "compression-vars: " `perl -V:z.*: ` " are here !"
compression-vars: zcat='' zip='zip' are here !
A leading colon removes the ``name='' part of the response, this allows you to map to the name you need. (mnemonic: empty label)
$ echo "goodvfork="`./perl -Ilib -V::usevfork`
goodvfork=false;
Leading and trailing colons can be used together if you need positional parameter values without the names. Note that in the case below, the "PERL_API" params are returned in alphabetical order.
$ echo building_on `perl -V::osname: -V::PERL_API_.*:` now
building_on 'linux' '5' '1' '9' now
This switch really just enables the global $^W variable; normally, the lexically scoped "use warnings" pragma is preferred. You can disable or promote into fatal errors specific warnings using "__WARN__" hooks, as described in perlvar and ``warn'' in perlfunc. See also perldiag and perltrap. A fine-grained warning facility is also available if you want to manipulate entire classes of warnings; see warnings.
Forbidden in ""PERL5OPT"".
All references to line numbers by the program (warnings, errors, ...) will treat the "#!" line as the first line. Thus a warning on the 2nd line of the program, which is on the 100th line in the file will be reported as line 2, not as line 100. This can be overridden by using the "#line" directive. (See ``Plain Old Comments (Not!)'' in perlsyn)
If a directory name is specified, Perl will switch to that directory before running the program. The -x switch controls only the disposal of leading garbage. The program must be terminated with "__END__" if there is trailing garbage to be ignored; the program can process any or all of the trailing garbage via the "DATA" filehandle if desired.
The directory, if specified, must appear immediately following the -x with no intervening whitespace.
If PERL5LIB is not defined, ``PERLLIB'' is used. Directories are separated (like in PATH) by a colon on Unixish platforms and by a semicolon on Windows (the proper path separator being given by the command "perl -V:path_sep").
When running taint checks, either because the program was running setuid or setgid, or the ``-T'' or ``-t'' switch was specified, neither PERL5LIB nor ``PERLLIB'' is consulted. The program should instead say:
use lib "/my/directory";
It is conventional to start layer names with a colon (for example, ":perlio") to emphasize their similarity to variable ``attributes''. But the code that parses layer specification strings, which is also used to decode the PERLIO environment variable, treats the colon as a separator.
An unset or empty PERLIO is equivalent to the default set of layers for your platform; for example, ":unix:perlio" on Unix-like systems and ":unix:crlf" on Windows and other DOS-like systems.
The list becomes the default for all Perl's IO. Consequently only built-in layers can appear in this list, as external layers (such as ":encoding()") need IO in order to load them! See ``open pragma'' for how to add external encodings as defaults.
Layers it makes sense to include in the PERLIO environment variable are briefly summarized below. For more details see PerlIO.
The default set of layers should give acceptable results on all platforms.
For Unix platforms that will be the equivalent of ``:unix:perlio'' or ``:stdio''. Configure is set up to prefer the ``:stdio'' implementation if the system's library provides for fast access to the buffer (not common on modern architectures); otherwise, it uses the ``:unix:perlio'' implementation.
On Win32 the default in this release (5.30) is ``:unix:crlf''. Win32's ``:stdio'' has a number of bugs/mis-features for Perl IO which are somewhat depending on the version and vendor of the C compiler. Using our own ":crlf" layer as the buffer avoids those issues and makes things more uniform.
This release (5.30) uses ":unix" as the bottom layer on Win32, and so still uses the C compiler's numeric file descriptor routines. There is an experimental native ":win32" layer, which is expected to be enhanced and may eventually become the default under Win32.
The PERLIO environment variable is completely ignored when Perl is run in taint mode.
% env PERLIO_DEBUG=/tmp/perlio.log perl -Di script ...
and under Win32, the approximately equivalent:
> set PERLIO_DEBUG=CON perl -Di script ...
This functionality is disabled for setuid scripts, for scripts run with ``-T'', and for scripts run on a Perl built without "-DDEBUGGING" support.
The PERLLIB environment variable is completely ignored when Perl is run in taint mode.
BEGIN { require "perl5db.pl" }
The PERL5DB environment variable is only used when Perl is started with a bare ``-d'' switch.
Note that Perl doesn't use COMSPEC for this purpose because COMSPEC has a high degree of variability among users, leading to portability concerns. Besides, Perl can use a shell that may not be fit for interactive use, and setting COMSPEC to such a shell may interfere with the proper functioning of other programs (which usually look in COMSPEC to find a shell fit for interactive use).
Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint checked when running external commands. It is recommended that you explicitly set (or delete) $ENV{PERL5SHELL} when running in taint mode under Windows.
Setting this environment variable to 1 means that Perl will simply use the first suitable LSP enumerated in the catalog, which keeps McAfee Guardian happy---and in that particular case Perl still works too because McAfee Guardian's LSP actually plays other games which allow applications requiring IFS compatibility to work.
If set, this dumps out memory statistics after execution. If set to an integer greater than one, also dumps out memory statistics after compilation.
If the option is provided, and "PERL_PERTURB_KEYS" is NOT set, then a value of '0' implies "PERL_PERTURB_KEYS=0" and any other value implies "PERL_PERTURB_KEYS=2".
PLEASE NOTE: The hash seed is sensitive information. Hashes are randomized to protect against local and remote attacks against Perl code. By manually setting a seed, this protection may be partially or completely lost.
See ``Algorithmic Complexity Attacks'' in perlsec, ``PERL_PERTURB_KEYS'', and ``PERL_HASH_SEED_DEBUG'' for more information.
When set to "1" or "RANDOM" then traversing keys will be randomized. Every time a hash is inserted into the key order will change in a random fashion. The order may not be repeatable in a following program run even if the PERL_HASH_SEED has been specified. This is the default mode for perl.
When set to "2" or "DETERMINISTIC" then inserting keys into a hash will cause the key order to change, but in a way that is repeatable from program run to program run.
NOTE: Use of this option is considered insecure, and is intended only for debugging non-deterministic behavior in Perl's hash function. Do not use it in production.
See ``Algorithmic Complexity Attacks'' in perlsec and ``PERL_HASH_SEED'' and ``PERL_HASH_SEED_DEBUG'' for more information. You can get and set the key traversal mask for a specific hash by using the "hash_traversal_mask()" function from Hash::Util.
Note that any information about the hash function, especially the hash seed is sensitive information: by knowing it, one can craft a denial-of-service attack against Perl code, even remotely; see ``Algorithmic Complexity Attacks'' in perlsec for more information. Do not disclose the hash seed to people who don't need to know it. See also "hash_seed()" and "hash_traversal_mask()".
An example output might be:
HASH_FUNCTION = ONE_AT_A_TIME_HARD HASH_SEED = 0x652e9b9349a7a032 PERTURB_KEYS = 1 (RANDOM)
$ 3>foo3 PERL_MEM_LOG=3m perl ...
Ignored if perl is run setuid or setgid. Used only for some limited startup randomization (hash keys) if "-T" or "-t" perl is started with tainting enabled.
Perl may be built to ignore this variable.
Perl also has environment variables that control how Perl handles data specific to particular natural languages; see perllocale.
Perl and its various modules and components, including its test frameworks, may sometimes make use of certain other environment variables. Some of these are specific to a particular platform. Please consult the appropriate module documentation and any documentation for your platform (like perlsolaris, perllinux, perlmacosx, perlwin32, etc) for variables peculiar to those specific situations.
Perl makes all environment variables available to the program being executed, and passes these along to any child processes it starts. However, programs 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 exists $ENV{SHELL};
delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};
Note that this section does not document what actually happens inside the perl interpreter, it documents what effectively happens.
perl -I 1 -I 2 -I 3
will first prepend 3 onto the front of @INC, then prepend 2, and then prepend 1. The result is that @INC begins with:
qw(1 2 3)
perl -Mlib=1 -Mlib=2 -Mlib=3
will first use the lib pragma to prepend 1 to @INC, then it will prepend 2, then it will prepend 3, resulting in an @INC that begins with:
qw(3 2 1)
PERL5LIB=1:2:3 perl
will result in an @INC that begins with:
qw(1 2 3)
PERL5LIB=e1:e2 perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
will result in an @INC that begins with:
qw(m2 m1 i1 i2 e1 e2)
After normal processing of "-I" switches from the command line, all the "-I" switches in "PERL5OPT" are extracted. They are processed from left to right instead of from right to left. Also note that while whitespace is allowed between a "-I" and its directory on the command line, it is not allowed in "PERL5OPT".
After normal processing of "-M" switches from the command line, all the "-M" switches in "PERL5OPT" are extracted. They are processed from left to right, i.e. the same as those on the command line.
An example may make this clearer:
export PERL5OPT="-Mlib=optm1 -Iopti1 -Mlib=optm2 -Iopti2"
export PERL5LIB=e1:e2
perl -I i1 -Mlib=m1 -I i2 -Mlib=m2
will result in an @INC that begins with:
qw(
optm2
optm1
m2
m1
opti2
opti1
i1
i2
e1
e2
)