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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 [nnuummbbeerr//lliisstt] ] [ -P ] [ -S ] [ -x[dir] ]
[ -i[extension] ] [ -e 'command' ] [ -- ] [ program-
file ] [ argument ]...
DESCRIPTION
The normal way to run a Perl program is by making it directly exe-
cutable, or else by passing the name of the source file as an argument
on the command line. (An interactive Perl environment is also possi-
ble--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 switches on the command line.
2. Contained in the file specified by the first filename on the com-
mand 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 pro-
gram 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 pro-
gram 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 behavior 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 pro-
gram. And a partial -I switch could also cause odd results.
Some switches do care if they are processed twice, for instance combi-
nations of -l and -0. Either put all the switches after the 32-charac-
ter 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 -wS $0 ${1+"$@"}'
if $running_under_some_shell;
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", 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 pro-
gram 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 "ALTER-
NATE_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 (includ-
ing building from the sources), you may have to modify the Registry
yourself. Note that this means you can no longer tell the differ-
ence between an executable Perl program and a Perl library file.
Macintosh
Under "Classic" MacOS, a perl program will have the appropriate
Creator and Type, so that double-clicking them will invoke the
MacPerl application. Under Mac OS X, clickable apps can be made
from any "#!" script using Wil Sanchez' DropScript utility:
http://www.wsanchez.net/software/ .
VMS Put
$ perl -mysw 'f$env("procedure")' 'p1' 'p2' 'p3' 'p4' 'p5' 'p6' 'p7' 'p8' !
$ exit++ + ++$status != 0 and $exit = $status = undef;
at the top of your program, where -mysw are any command line
switches you want to pass to Perl. You can now invoke the program
directly, by saying "perl program", or as a DCL procedure, by say-
ing @program (or implicitly via DCL$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\""
# Macintosh
print "Hello world\n"
(then Run "Myscript" or Shift-Command-R)
# 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 "Hello world\n""
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.
Under the Macintosh, it depends which environment you are using. The
MacPerl shell, or MPW, is much like Unix shells in its support for sev-
eral quoting variants, except that it makes free use of the Macintosh's
non-ASCII characters as control characters.
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 eas-
ily 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 pro-
gram 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 clus-
tered 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 hexadeci-
mal 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. The value 0777 will cause Perl to slurp files whole because
there is no legal byte with that value.
If you want to specify any Unicode character, use the hexadecimal
format: "-0xHHH...", where the "H" are valid hexadecimal digits.
(This means that you cannot use the "-x" with a directory name
that consists of hexadecimal digits.)
-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 [nnuummbbeerr//lliisstt]
The "-C" flag controls some Unicode 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 num-
bers.
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
For example, "-COE" and "-C6" will both turn on UTF-8-ness on both
STDOUT and STDERR. Repeating letters is just redundant, not cumu-
lative nor toggling.
The "io" options mean that any subsequent open() (or similar I/O
operations) 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.
You can use "-C0" (or "0" for "PERL_UNICODE") to explicitly dis-
able all the above Unicode features.
The read-only magic variable "${^UNICODE}" reflects the numeric
value of this setting. This is 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".)
-c causes Perl to check the syntax of the program and then exit with-
out executing it. Actually, it will execute "BEGIN", "CHECK", and
"use" blocks, because 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:foo[=bar,baz]
-dt:foo[=bar,baz]
runs the program under the control of a debugging, profiling, or
tracing module installed as Devel::foo. E.g., -d:DProf executes
the program using the Devel::DProf profiler. As with the -M flag,
options may be passed to the Devel::foo package where they will be
received and interpreted by the Devel::foo::import routine. 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
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, preprocessor command for -P, source file input state
128 m Memory allocation
256 f Format processing
512 r Regular expression parsing and execution
1024 x Syntax tree dump
2048 u Tainting checks
4096 (Obsolete, previously used for LEAKTEST)
8192 H Hash dump -- usurps values()
16384 X Scratchpad allocation
32768 D Cleaning up
65536 S Thread synchronization
131072 T Tokenising
262144 R Include reference counts of dumped variables (eg when using -Ds)
524288 J Do not s,t,P-debug (Jump over) opcodes within package DB
1048576 v Verbose: use in conjunction with other flags
8388608 q quiet - currently only suppresses the "EXECUTING" message
All these flags require -DDEBUGGING when you compile the Perl exe-
cutable (but see Devel::Peek, 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 "Con-
figure" 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.
-f Disable executing $Config{sitelib}/sitecustomize.pl at startup.
Perl can be built so that it by default will try to execute $Con-
fig{sitelib}/sitecustomize.pl at startup. This is a hook that
allows the sysadmin to customize how perl behaves. It can for
instance be used to add entries to the @INC array to make perl
find modules in non-standard locations.
-Fpattern
specifies the pattern to split on if -a is also in effect. The
pattern may be surrounded by "//", "", or '', otherwise it will be
put in single quotes. You can't use literal whitespace in the pat-
tern.
-h prints a summary of the options.
-i[extension]
specifies that files processed by the "<>" construct are to be
edited in-place. It does this by renaming the input file, opening
the output file by the original name, and selecting that output
file as the default for print() statements. The extension, if
supplied, is used to modify the name of the old file to make a
backup copy, following these rules:
If no extension is supplied, no backup is made and the current
file is overwritten.
If the extension doesn't contain a "*", then it is appended to the
end of the current filename as a suffix. If the extension does
contain one or more "*" characters, then each "*" is replaced with
the current filename. In Perl terms, you could think of this as:
($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 con-
tinue 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), and also tells the C preprocessor where to search
for include files. The C preprocessor is invoked with -P; by
default it searches /usr/include and /usr/lib/perl.
-l[octnum]
enables automatic line-ending processing. It has two separate
effects. First, it automatically chomps $/ (the input record sep-
arator) when used with -n or -p. Second, it assigns "$\" (the
output record separator) to have the value of octnum so that any
print statements will have that separator added back on. If oct-
num 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 pro-
cessed, 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 pro-
gram.
-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 -mmod-
ule=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 dis-
tinction between -m and -M.
A consequence of this is that -MFoo=number never does a version
check (unless "Foo::import()" itself is set up to do a version
check, which could happen for example if Foo 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.
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.
-P NOTE: Use of -P is strongly discouraged because of its inherent
problems, including poor portability.
This option causes your program to be run through the C preproces-
sor before compilation by Perl. Because both comments and cpp
directives begin with the # character, you should avoid starting
comments with any words recognized by the C preprocessor such as
"if", "else", or "define".
If you're considering using "-P", you might also want to look at
the Filter::cpp module from CPAN.
The problems of -P include, but are not limited to:
* The "#!" line is stripped, so any switches there don't
apply.
* A "-P" on a "#!" line doesn't work.
* All lines that begin with (whitespace and) a "#" but do
not look like cpp commands, are stripped, including any-
thing inside Perl strings, regular expressions, and
here-docs .
* In some platforms the C preprocessor knows too much: it
knows about the C++ -style until-end-of-line comments
starting with "//". This will cause problems with com-
mon Perl constructs like
s/foo//;
because after -P this will became illegal code
s/foo
The workaround is to use some other quoting separator
than "/", like for example "!":
s!foo!!;
* It requires not only a working C preprocessor but also a
working sed. If not on UNIX, you are probably out of
luck on this.
* Script line numbers are not preserved.
* The "-x" does not work with "-P".
-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 "strict refs". Also, when using this
option on a script with warnings enabled you may get a lot of spu-
rious "used only once" warnings.
-S makes Perl use the PATH environment variable to search for the
program (unless the name of the program contains directory separa-
tors).
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 pro-
gresses.
Typically this is used to emulate #! startup on platforms that
don't support #!. Its 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 $running_under_some_shell is never true. If the pro-
gram will be interpreted by csh, you will need to replace
"${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 con-
struct 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 (i.e., 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 be controlled normally with "no warn-
ings qw(taint)".
NOTE: this is not a substitute for -T. This is meant only to be
used 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 forces "taint" checks to be turned on so you can test them. Ordi-
narily 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 obsolete 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 sup-
plied). 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.
This switch has been superseded in favor of the new Perl code gen-
erator backends to the compiler. See B and B::Bytecode for
details.
-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 the -w switch (or the $^W vari-
able) must be used 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 cur-
rent 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 ';', allow-
ing 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 posi-
tional 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
that are mentioned only once and scalar variables that are used
before being set, redefined subroutines, references to undefined
filehandles or filehandles opened read-only that you are attempt-
ing to write on, values used as a number that don't look like num-
bers, using an array as though it were a scalar, if your subrou-
tines recurse more than 100 deep, and innumerable other things.
This switch really just enables the internal $^W variable. 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 new, 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 per-
llexwarn.
-X Disables all warnings regardless of "use warnings" or $^W. See
perllexwarn.
-x
-x directory
tells Perl that the program is embedded in a larger chunk of unre-
lated ASCII 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. 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 termi-
nated 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).
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 cur-
rent directory. Any architecture-specific directories
under the specified locations are automatically included if
they exist. 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 switch was used), nei-
ther variable is used. The program should instead say:
use lib "/my/directory";
PERL5OPT Command-line options (switches). Switches in this variable
are taken as if they were on every Perl command line. Only
the -[DIMUdmtw] switches are allowed. When running taint
checks (because the program was running setuid or setgid,
or the -T switch was used), this variable is ignored. If
PERL5OPT begins with -T, tainting will be enabled, and any
subsequent options ignored.
PERLIO A space (or colon) separated list of PerlIO layers. If perl
is built to use PerlIO system for IO (the default) these
layers effect perl's IO.
It is conventional to start layer names with a colon e.g.
":perlio" to emphasise their similarity to variable
"attributes". But the code that parses layer specification
strings (which is also used to decode the PERLIO environ-
ment variable) treats the colon as a separator.
An unset or empty PERLIO is equivalent to ":stdio".
The list becomes the default for all perl's IO. Conse-
quently 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.
The layers that it makes sense to include in the PERLIO
environment variable are briefly summarised below. For more
details see PerlIO.
:bytes A pseudolayer that turns off the ":utf8" flag 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 ":per-
lio:bytes".
:crlf A layer which does CRLF to "\n" translation distin-
guishing "text" and "binary" files in the manner of
MS-DOS and similar operating systems. (It cur-
rently does not mimic MS-DOS as far as treating of
Control-Z as being an end-of-file marker.)
:mmap A layer which implements "reading" of files by
using "mmap()" to make (whole) 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" buffer-
ing 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 top-
most layer. Use with the same care as is reserved
for nitroglycerin.
: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 any translation. In particular CRLF
translation, and/or :utf8 intuited from locale are
disabled.
Unlike in the 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 PerlIO interface by wrapping
system's ANSI C "stdio" library calls. The layer
provides both buffering and IO. Note that ":stdio"
layer does not do CRLF translation even if that is
platforms normal behaviour. You will need a ":crlf"
layer above it to do that.
:unix Low level layer which calls "read", "write" and
"lseek" etc.
:utf8 A pseudolayer that turns on a flag on the layer
below to tell perl that output should be in utf8
and that input should be regarded as already in
utf8 form. May be useful in PERLIO environment
variable to make UTF-8 the default. (To turn off
that behaviour use ":bytes" layer.)
:win32 On Win32 platforms this experimental layer uses
native "handle" IO rather than unix-like numeric
file descriptor layer. Known to be buggy in this
release.
On all platforms the default set of layers should give
acceptable results.
For UNIX platforms that will equivalent of "unix perlio" or
"stdio". Configure is setup to prefer "stdio" implementa-
tion if system's library provides for fast access to the
buffer, otherwise it uses the "unix perlio" implementation.
On Win32 the default in this release is "unix crlf".
Win32's "stdio" has a number of bugs/mis-features for perl
IO which are somewhat C compiler vendor/version dependent.
Using our own "crlf" layer as the buffer avoids those
issues and makes things more uniform. The "crlf" layer
provides CRLF to/from "\n" conversion as well as buffering.
This release uses "unix" as the bottom layer on Win32 and
so still uses C compiler's numeric file descriptor rou-
tines. There is an experimental native "win32" layer which
is expected to be enhanced and should eventually be the
default under Win32.
PERLIO_DEBUG
If set to the name of a file or device then certain opera-
tions of PerlIO sub-system will be logged to that file
(opened as append). Typical uses are UNIX:
PERLIO_DEBUG=/dev/tty perl script ...
and Win32 approximate 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 cur-
rent directory. If PERL5LIB is defined, PERLLIB is not
used.
PERL5DB The command used to load the debugger code. The default
is:
BEGIN { require 'perl5db.pl' }
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)
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 to be space-sep-
arated. Precede any character that needs to be protected
(like a space or backslash) with a backslash.
Note that Perl doesn't use COMSPEC for this purpose because
COMSPEC has a high degree of variability among users, lead-
ing to portability concerns. Besides, perl can use a shell
that may not be fit for interactive use, and setting COM-
SPEC to such a shell may interfere with the proper func-
tioning of other programs (which usually look in COMSPEC to
find a shell fit for interactive use).
PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
Set to 1 to allow the use of non-IFS compatible LSP's.
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 all
applications to use its LSP 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 cata-
log, which keeps McAfee Guardian happy (and in that partic-
ular case Perl still works too because McAfee Guardian's
LSP actually plays some other games which allow applica-
tions 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_mymal-
loc" is 'define'). If set, this causes memory statistics
to be dumped after execution. If set to an integer greater
than one, also causes memory statistics to be dumped after
compilation.
PERL_DESTRUCT_LEVEL
Relevant only if your perl executable was built with -DDE-
BUGGING, this controls the behavior of global destruction
of objects and other references. See "PERL_DESTRUCT_LEVEL"
in perlhack for more information.
PERL_DL_NONLAZY
Set to one 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 it.
PERL_ENCODING
If using the "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 randomise Perl's internal hash
function. To emulate the pre-5.8.1 behaviour, set to an
integer (zero means exactly the same order as 5.8.0).
"Pre-5.8.1" means, among other things, that hash keys will
be ordered the same between different runs of Perl.
The default behaviour is to randomise unless the
PERL_HASH_SEED is set. If Perl has been compiled with
"-DUSE_HASH_SEED_EXPLICIT", the default behaviour is not to
randomise 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. This means that each different run
of Perl will have a different ordering of the results of
keys(), values(), and each().
Please note that 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 one 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 behavior caused by hash random-
ization.
Note that the hash seed is sensitive information: by know-
ing 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() of Hash::Util.
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 PERL-
SHR, PERL_ENV_TABLES, and SYS$TIMEZONE_DIFFERENTIAL but are
optional and discussed further in perlvms and in README.vms
in the Perl source distribution.
PERL_SIGNALS
In Perls 5.8.1 and later. If set to "unsafe" the
pre-Perl-5.8.0 signals behaviour (immediate but unsafe) is
restored. If set to "safe" the safe (or deferred) signals
are used. See "Deferred Signals (Safe Signals)" in per-
lipc.
PERL_UNICODE
Equivalent to the -C command-line switch. Note that this
is not a boolean variable-- setting this to "1" is not the
right way to "enable Unicode" (whatever that would mean).
You can use "0" to "disable Unicode", though (or alterna-
tively unset PERL_UNICODE in your shell before starting
Perl). See the description of the "-C" switch for more
information.
SYS$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.
Apart from these, Perl uses no other environment variables, except to
make them available to the program being executed, and to child pro-
cesses. 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 v5.8.8 2006-01-07 PERLRUN(1)
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