PERLRUN(1) Perl Programmers Reference Guide PERLRUN(1)
NAME
perlrun - how to execute the Perl interpreter
SYNOPSIS
perl [ -sTtuUWX ] [ -hv ] [ -V[:configvar] ]
[ -cw ] [ -d[t][:debugger] ] [ -D[number/list] ]
[ -pna ] [ -Fpattern ] [ -l[octal] ] [ -0[octal/hexadecimal] ]
[ -Idir ] [ -m[-]module ] [ -M[-]'module...' ] [ -f ]
[ -C [number/list] ] [ -S ] [ -x[dir] ]
[ -i[extension] ]
[ [-e|-E] 'command' ] [ -- ] [ programfile ] [ argument ]...
DESCRIPTION
The normal way to run a Perl program is by making it directly
executable, or else by passing the name of the source file as an
argument on the command line. (An interactive Perl environment is also
possible--see perldebug for details on how to do that.) Upon startup,
Perl looks for your program in one of the following places:
1. Specified line by line via -e or -E switches on the command line.
2. Contained in the file specified by the first filename on the
command line. (Note that systems supporting the "#!" notation
invoke interpreters this way. See "Location of Perl".)
3. Passed in implicitly via standard input. This works only if there
are no filename arguments--to pass arguments to a STDIN-read
program you must explicitly specify a "-" for the program name.
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-*-
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, perl5.005_57, 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.
#! and quoting on non-Unix systems
Unix's "#!" technique can be simulated on other systems:
OS/2
Put
extproc perl -S -your_switches
as the first line in "*.cmd" file (-S due to a bug in cmd.exe's
`extproc' handling).
MS-DOS
Create a batch file to run your program, and codify it in
"ALTERNATE_SHEBANG" (see the dosish.h file in the source
distribution for more information).
Win95/NT
The Win95/NT installation, when using the ActiveState installer for
Perl, will modify the Registry to associate the .pl extension with
the perl interpreter. If you install Perl by other means
(including building from the sources), you may have to modify the
Registry yourself. Note that this means you can no longer tell the
difference between an executable Perl program and a Perl library
file.
VMS Put
$ 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.
Location of Perl
It may seem obvious to say, but Perl is useful only when users can
easily find it. When possible, it's good for both /usr/bin/perl and
/usr/local/bin/perl to be symlinks to the actual binary. If that can't
be done, system administrators are strongly encouraged to put (symlinks
to) perl and its accompanying utilities into a directory typically
found along a user's PATH, or in some other obvious and convenient
place.
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/perl5.00554
or if you just want to be running at least version, place a statement
like this at the top of your program:
use 5.005_54;
Command Switches
As with all standard commands, a single-character switch may be
clustered with the following switch, if any.
#!/usr/bin/perl -spi.orig # same as -s -p -i.orig
Switches include:
-0[octal/hexadecimal]
specifies the input record separator ($/) as an octal or
hexadecimal number. If there are no digits, the null character is
the separator. Other switches may precede or follow the digits.
For example, if you have a version of find which can print
filenames terminated by the null character, you can say this:
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.)
-a turns on autosplit mode when used with a -n or -p. An implicit
split command to the @F array is done as the first thing inside
the implicit while loop produced by the -n or -p.
perl -ane 'print pop(@F), "\n";'
is equivalent to
while (<>) {
@F = split(' ');
print pop(@F), "\n";
}
An alternate delimiter may be specified using -F.
-C [number/list]
The -C flag controls some of the Perl Unicode features.
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_TYPE, and LANG, in the order of
decreasing precedence) -- if the variables indicate
UTF-8, then the selected "IOEioA" are in effect
a 256 Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
code in debugging mode.
For example, -COE and -C6 will both turn on UTF-8-ness on both
STDOUT and STDERR. Repeating letters is just redundant, not
cumulative nor toggling.
The "io" options mean that any subsequent open() (or similar I/O
operations) in the current file scope will have the ":utf8" PerlIO
layer implicitly applied to them, in other words, UTF-8 is
expected from any input stream, and UTF-8 is produced to any
output stream. This is just the default, with explicit layers in
open() and with binmode() one can manipulate streams as usual.
-C on its own (not followed by any number or option list), or the
empty string "" for the "PERL_UNICODE" environment variable, has
the same effect as -CSDL. In other words, the standard I/O
handles and the default "open()" layer are UTF-8-fied but only if
the locale environment variables indicate a UTF-8 locale. This
behaviour follows the implicit (and problematic) UTF-8 behaviour
of Perl 5.8.0. (See "UTF-8 no longer default under UTF-8 locales"
in perl581delta.)
You can use -C0 (or "0" for "PERL_UNICODE") to explicitly disable
all the above Unicode features.
The read-only magic variable "${^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.
-c causes Perl to check the syntax of the program and then exit
without executing it. Actually, it will execute and "BEGIN",
"UNITCHECK", or "CHECK" blocks and any "use" statements: these are
considered as occurring outside the execution of your program.
"INIT" and "END" blocks, however, will be skipped.
-d
-dt runs the program under the Perl debugger. See perldebug. If t is
specified, it indicates to the debugger that threads will be used
in the code being debugged.
-d:MOD[=bar,baz]
-dt:MOD[=bar,baz]
runs the program under the control of a debugging, profiling, or
tracing module installed as "Devel::MOD". E.g., -d:DProf executes
the program using the "Devel::DProf" profiler. As with the -M
flag, options may be passed to the "Devel::MOD" package where they
will be received and interpreted by the "Devel::MOD::import"
routine. Again, like -M, use --d:-MOD to call
"Devel::MOD::unimport" instead of import. The comma-separated
list of options must follow a "=" character. If t is specified,
it indicates to the debugger that threads will be used in the code
being debugged. See perldebug.
-Dletters
-Dnumber
sets debugging flags. To watch how it executes your program, use
-Dtls. (This works only if debugging is compiled into your Perl.)
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)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
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
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
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. This flag is automatically set
if you include -g option when "Configure" asks you about
optimizer/debugger flags.
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.
-e commandline
may be used to enter one line of program. If -e is given, Perl
will not look for a filename in the argument list. Multiple -e
commands may be given to build up a multi-line script. Make sure
to use semicolons where you would in a normal program.
-E commandline
behaves just like -e, except that it implicitly enables all
optional features (in the main compilation unit). See feature.
-f Disable executing $Config{sitelib}/sitecustomize.pl at startup.
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 $Config{usesitecustomize}.
-Fpattern
specifies the pattern to split on if -a is also in effect. The
pattern may be surrounded by "//", "", or '', otherwise it will be
put in single quotes. You can't use literal whitespace in the
pattern.
-h prints a summary of the options.
-i[extension]
specifies that files processed by the "<>" construct are to be
edited in-place. It does this by renaming the input file, opening
the output file by the original name, and selecting that output
file as the default for print() statements. The extension, if
supplied, is used to modify the name of the old file to make a
backup copy, following these rules:
If no extension is supplied, no backup is made and the current
file is overwritten.
If the extension doesn't contain a "*", then it is appended to the
end of the current filename as a suffix. If the extension does
contain one or more "*" characters, then each "*" is replaced with
the current filename. In Perl terms, you could think of this as:
($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.
-Idirectory
Directories specified by -I are prepended to the search path for
modules (@INC).
-l[octnum]
enables automatic line-ending processing. It has two separate
effects. First, it automatically chomps $/ (the input record
separator) when used with -n or -p. Second, it assigns "$\" (the
output record separator) to have the value of octnum so that any
print statements will have that separator added back on. If
octnum is omitted, sets "$\" to the current value of $/. For
instance, to trim lines to 80 columns:
perl -lpe 'substr($_, 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.
-m[-]module
-M[-]module
-M[-]'module ...'
-[mM][-]module=arg[,arg]...
-mmodule executes "use" module "();" before executing your
program.
-Mmodule executes "use" module ";" before executing your program.
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'.
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.
A consequence of this 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.
-n causes Perl to assume the following loop around your program,
which makes it iterate over filename arguments somewhat like sed
-n or awk:
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. 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.
-p causes Perl to assume the following loop around your program,
which makes it iterate over filename arguments somewhat like sed:
LINE:
while (<>) {
... # your program goes here
} continue {
print or die "-p destination: $!\n";
}
If a file named by an argument cannot be opened for some reason,
Perl warns you about it, and moves on to the next file. Note that
the lines are printed automatically. An error occurring during
printing is treated as fatal. To suppress printing use the -n
switch. A -p overrides a -n switch.
"BEGIN" and "END" blocks may be used to capture control before or
after the implicit loop, just as in awk.
-s enables rudimentary switch parsing for switches on the command
line after the program name but before any filename arguments (or
before an argument of --). Any switch found there is removed from
@ARGV and sets the corresponding variable in the Perl program.
The following program prints "1" if the program is invoked with a
-xyz switch, and "abc" if it is invoked with -xyz=abc.
#!/usr/bin/perl -s
if ($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.
-S makes Perl use the PATH environment variable to search for the
program unless the name of the program contains path separators.
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.
-t Like -T, but taint checks will issue warnings rather than fatal
errors. These warnings can now be controlled normally with "no
warnings qw(taint)".
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.
-T turns on "taint" so you can test them. Ordinarily these checks
are done only when running setuid or setgid. It's a good idea to
turn them on explicitly for programs that run on behalf of someone
else whom you might not necessarily trust, such as CGI programs or
any internet servers you might write in Perl. See perlsec for
details. For security reasons, this option must be seen by Perl
quite early; usually this means it must appear early on the
command line or in the "#!" line for systems which support that
construct.
-u This switch causes Perl to dump core after compiling your program.
You can then in theory take this core dump and turn it into an
executable file by using the 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 want to
execute a portion of your program 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.
-U allows Perl to do unsafe operations. Currently the only "unsafe"
operations are attempting to unlink directories while running as
superuser and running setuid programs with fatal taint checks
turned into warnings. Note that warnings must be enabled along
with this option to actually generate the taint-check warnings.
-v prints the version and patchlevel of your perl executable.
-V prints summary of the major perl configuration values and the
current values of @INC.
-V:configvar
Prints to STDOUT the value of the named configuration variable(s),
with multiples when your "configvar" argument looks like a regex
(has non-letters). For example:
$ 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
-w prints warnings about dubious constructs, such as variable names
mentioned only once and scalar variables used before being set;
redefined subroutines; references to undefined filehandles;
filehandles opened read-only that you are attempting to write on;
values used as a number that don't look like numbers; using an
array as though it were a scalar; if your subroutines recurse more
than 100 deep; and innumerable other things.
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 or perllexwarn.
-W Enables all warnings regardless of "no warnings" or $^W. See
perllexwarn.
-X Disables all warnings regardless of "use warnings" or $^W. See
perllexwarn.
-x
-xdirectory
tells Perl that the program is embedded in a larger chunk of
unrelated text, such as in a mail message. Leading garbage will
be discarded until the first line that starts with "#!" and
contains the string "perl". Any meaningful switches on that line
will be applied.
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.
ENVIRONMENT
HOME Used if "chdir" has no argument.
LOGDIR Used if "chdir" has no argument and HOME is not set.
PATH Used in executing subprocesses, and in finding the program
if -S is used.
PERL5LIB A list of directories in which to look for Perl library
files before looking in the standard library and the
current directory. Any architecture-specific directories
under the specified locations are automatically included if
they exist, with this lookup done at interpreter startup
time.
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";
PERL5OPT Command-line options (switches). Switches in this variable
are treated as if they were on every Perl command line.
Only the -[CDIMUdmtwW] switches are allowed. When running
taint checks (either because the program was running setuid
or setgid, or because the -T or -t switch was used), this
variable is ignored. If PERL5OPT begins with - T, tainting
will be enabled and subsequent options ignored. If
PERL5OPT begins with -t, tainting will be enabled, a
writable dot removed from @INC, and subsequent options
honored.
PERLIO A space (or colon) separated list of PerlIO layers. If perl
is built to use PerlIO system for IO (the default) these
layers affect Perl's IO.
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.
:bytes A pseudolayer that turns the ":utf8" flag off for
the layer below; unlikely to be useful on its own
in the global PERLIO environment variable. You
perhaps were thinking of ":crlf:bytes" or
":perlio:bytes".
:crlf A layer which does CRLF to "\n" translation
distinguishing "text" and "binary" files in the
manner of MS-DOS and similar operating systems.
(It currently does not mimic MS-DOS as far as
treating of Control-Z as being an end-of-file
marker.)
:mmap A layer that implements "reading" of files by using
mmap(2) to make an entire file appear in the
process's address space, and then using that as
PerlIO's "buffer".
:perlio This is a re-implementation of stdio-like buffering
written as a PerlIO layer. As such it will call
whatever layer is below it for its operations,
typically ":unix".
:pop An experimental pseudolayer that removes the
topmost layer. Use with the same care as is
reserved for nitroglycerine.
:raw A pseudolayer that manipulates other layers.
Applying the ":raw" layer is equivalent to calling
"binmode($fh)". It makes the stream pass each byte
as-is without translation. In particular, both
CRLF translation and intuiting ":utf8" from the
locale are disabled.
Unlike in earlier versions of Perl, ":raw" is not
just the inverse of ":crlf": other layers which
would affect the binary nature of the stream are
also removed or disabled.
:stdio This layer provides a PerlIO interface by wrapping
system's ANSI C "stdio" library calls. The layer
provides both buffering and IO. Note that the
":stdio" layer does not do CRLF translation even if
that is the platform's normal behaviour. You will
need a ":crlf" layer above it to do that.
:unix Low-level layer that calls "read", "write",
"lseek", etc.
:utf8 A pseudolayer that enables a flag in the layer
below to tell Perl that output should be in utf8
and that input should be regarded as already in
valid utf8 form. WARNING: It does not check for
validity and as such should be handled with extreme
caution for input, because security violations can
occur with non-shortest UTF-8 encodings, etc.
Generally ":encoding(utf8)" is the best option when
reading UTF-8 encoded data.
:win32 On Win32 platforms this experimental layer uses
native "handle" IO rather than a Unix-like numeric
file descriptor layer. Known to be buggy in this
release (5.14).
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; otherwise, it uses the "unix
perlio" implementation.
On Win32 the default in this release (5.14) 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. The
"crlf" layer provides CRLF conversion as well as buffering.
This release (5.14) 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 should
eventually become the default under Win32.
The PERLIO environment variable is completely ignored when
Perl is run in taint mode.
PERLIO_DEBUG
If set to the name of a file or device, certain operations
of PerlIO subsystem will be logged to that file, which is
opened in append mode Typical uses are in Unix:
% env PERLIO_DEBUG=/dev/tty perl script ...
and under Win32, the approximately equivalent:
> set PERLIO_DEBUG=CON
perl script ...
This functionality is disabled for setuid scripts and for
scripts run with -T.
PERLLIB A list of directories in which to look for Perl library
files before looking in the standard library and the
current directory. If PERL5LIB is defined, PERLLIB is not
used.
The PERLLIB environment variable is completely ignored when
Perl is run in taint mode.
PERL5DB The command used to load the debugger code. The default
is:
BEGIN { require "perl5db.pl" }
The PERL5DB environment variable is only used when Perl is
started with a bare -d switch.
PERL5DB_THREADED
If set to a true value, indicates to the debugger that the
code being debugged uses threads.
PERL5SHELL (specific to the Win32 port)
On Win32 ports only, may be set to an alternative shell
that Perl must use internally for executing "backtick"
commands or system(). Default is "cmd.exe /x/d/c" on
WindowsNT and "command.com /c" on Windows95. The value is
considered space-separated. Precede any character that
needs to be protected, like a space or backslash, with
another backslash.
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.
PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
Set to 1 to allow the use of non-IFS compatible LSPs
(Layered Service Providers). Perl normally searches for an
IFS-compatible LSP because this is required for its
emulation of Windows sockets as real filehandles. However,
this may cause problems if you have a firewall such as
McAfee Guardian, which requires that all applications use
its LSP but which is not IFS-compatible, because clearly
Perl will normally avoid using such an LSP.
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.
PERL_DEBUG_MSTATS
Relevant only if Perl is compiled with the "malloc"
included with the Perl distribution; that is, if "perl
-V:d_mymalloc" is "define".
If set, this dumps out memory statistics after execution.
If set to an integer greater than one, also dumps out
memory statistics after compilation.
PERL_DESTRUCT_LEVEL
Relevant only if your Perl executable was built with
-DDEBUGGING, this controls the behaviour of global
destruction of objects and other references. See
"PERL_DESTRUCT_LEVEL" in perlhacktips for more information.
PERL_DL_NONLAZY
Set to "1" to have Perl resolve all undefined symbols when
it loads a dynamic library. The default behaviour is to
resolve symbols when they are used. Setting this variable
is useful during testing of extensions, as it ensures that
you get an error on misspelled function names even if the
test suite doesn't call them.
PERL_ENCODING
If using the "use encoding" pragma without an explicit
encoding name, the PERL_ENCODING environment variable is
consulted for an encoding name.
PERL_HASH_SEED
(Since Perl 5.8.1.) Used to randomize Perl's internal hash
function. To emulate the pre-5.8.1 behaviour, set to an
integer; "0" means exactly the same order as in 5.8.0.
"Pre-5.8.1" means, among other things, that hash keys will
always have the same ordering between different runs of
Perl.
Most hashes by default return elements in the same order as
in Perl 5.8.0. On a hash by hash basis, if pathological
data is detected during a hash key insertion, then that
hash will switch to an alternative random hash seed.
The default behaviour is to randomize unless the
PERL_HASH_SEED is set. If Perl has been compiled with
-DUSE_HASH_SEED_EXPLICIT, the default behaviour is not to
randomize unless the PERL_HASH_SEED is set.
If PERL_HASH_SEED is unset or set to a non-numeric string,
Perl uses the pseudorandom seed supplied by the operating
system and libraries.
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 and
"PERL_HASH_SEED_DEBUG" for more information.
PERL_HASH_SEED_DEBUG
(Since Perl 5.8.1.) Set to "1" to display (to STDERR) the
value of the hash seed at the beginning of execution.
This, combined with "PERL_HASH_SEED" is intended to aid in
debugging nondeterministic behaviour caused by hash
randomization.
Note that 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() in Hash::Util.
PERL_MEM_LOG
If your Perl was configured with -Accflags=-DPERL_MEM_LOG,
setting the environment variable "PERL_MEM_LOG" enables
logging debug messages. The value has the form
"<number>[m][s][t]", where "number" is the file descriptor
number you want to write to (2 is default), and the
combination of letters specifies that you want information
about (m)emory and/or (s)v, optionally with (t)imestamps.
For example, "PERL_MEM_LOG=1mst" logs all information to
stdout. You can write to other opened file descriptors in a
variety of ways:
$ 3>foo3 PERL_MEM_LOG=3m perl ...
PERL_ROOT (specific to the VMS port)
A translation-concealed rooted logical name that contains
Perl and the logical device for the @INC path on VMS only.
Other logical names that affect Perl on VMS include
PERLSHR, PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL,
but are optional and discussed further in perlvms and in
README.vms in the Perl source distribution.
PERL_SIGNALS
Available in Perls 5.8.1 and later. If set to "unsafe",
the pre-Perl-5.8.0 signal behaviour (which is immediate but
unsafe) is restored. If set to "safe", then safe (but
deferred) signals are used. See "Deferred Signals (Safe
Signals)" in perlipc.
PERL_UNICODE
Equivalent to the -C command-line switch. Note that this
is not a boolean variable. Setting this to "1" is not the
right way to "enable Unicode" (whatever that would mean).
You can use "0" to "disable Unicode", though (or
alternatively unset PERL_UNICODE in your shell before
starting Perl). See the description of the -C switch for
more information.
SYS$LOGIN (specific to the VMS port)
Used if chdir has no argument and HOME and LOGDIR are not
set.
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)};
perl v5.16.3 2013-03-04 PERLRUN(1)
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