r1 - 04 Mar 2006 - NelsonFerraz

ENVIRONMENT

NAME

perlrun - how to execute the Perl interpreter

SYNOPSIS

perl [ -sTtuUWX ]

        S<[ B<-hv> ] [ B<-V>[:I<configvar>] ]>

        S<[ B<-cw> ] [ B<-d>[B<t>][:I<debugger>] ] [ B<-D>[I<number/list>] ]>

        S<[ B<-pna> ] [ B<-F>I<pattern> ] [ B<-l>[I<octal>] ] [ B<-0>[I<octal/hexadecimal>] ]>

        S<[ B<-I>I<dir> ] [ B<-m>[B<->]I<module> ] [ B<-M>[B<->]I<'module...'> ]>

        S<[ B<-P> ]>

        S<[ B<-S> ]>

        S<[ B<-x>[I<dir>] ]>

        S<[ B<-i>[I<extension>] ]>

        S<[ B<-e> I<'command'> ] [ B<--> ] [ I<programfile> ] [ I<argument> ]...>

        S<[ B<-C [I<number/list>] >]> ]>

voltar para o topo

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 the perldebug manpage for details on how to do that.) Upon startup, Perl looks for your program in one of the following places:

-e

Location of Perl

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 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 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 -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 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.

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 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\""

    # 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 <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. Under the Macintosh, it depends which environment you are using. The MacPerl? shell, or MPW, is much like Unix shells in its support for several 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 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.

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 [number/list]

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 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

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) 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

disable 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 the perlfunc manpage), the two-arg binmode() (see binmode in the perlfunc manpage),

and the open pragma (see the open manpage).

(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 without

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 the perldebug manpage.

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 the perldebug manpage.

-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 the perldebguts manpage.

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

executable (but see the Devel::Peek manpage, the re manpage 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 the perldebug manpage 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{siteperl}/sitecustomize.pl at

startup.

Perl can be built so that it by default will try to execute

$Config{siteperl}/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.

-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...

    $ 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 the perlfunc manpage).

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 the perlfaq5 manpage.

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

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.

-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 preprocessor 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:

#!

-P

#!

All

#

"//"

    s/foo//;

    s/foo

"/"

"!"

    s!foo!!;

sed

-x

-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 --). This means you can have switches with two leading

dashes (--help). 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 --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 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 directory 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 #!. 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 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 (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 warnings

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. 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

the perlsec manpage 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 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.

This switch has been superseded in favor of the new Perl code

generator backends to the compiler. See the B manpage and the B::Bytecode manpage

for details.

-U

allows Perl to do unsafe operations. Currently the only ``unsafe''

operations are the unlinking of directories while running as superuser,

and running setuid programs with fatal taint checks turned into

warnings. Note that the -w switch (or the $^W variable) 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 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

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 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 internal $^W variable. You

can disable or promote into fatal errors specific warnings using

__WARN__ hooks, as described in the perlvar manpage and warn in the perlfunc manpage.

See also the perldiag manpage and the perltrap manpage. A new, fine-grained warning

facility is also available if you want to manipulate entire classes

of warnings; see the warnings manpage or the perllexwarn manpage.

-W

Enables all warnings regardless of no warnings or $^W.

See the perllexwarn manpage.

-X

Disables all warnings regardless of use warnings or $^W.

See the perllexwarn manpage.

-x

-x directory

tells Perl that the program is embedded in a larger chunk of unrelated

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 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).

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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. 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), neither 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

environment 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. 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.

The layers that it makes sense to include in the PERLIO environment

variable are briefly summarised below. For more details see the PerlIO ? manpage.

: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 :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 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'' 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 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.

crlfcrlfunixwin32

PERLIO_DEBUG

If set to the name of a file or device then certain operations 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 current 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-separated. 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, 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).

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 catalog, which keeps McAfee? Guardian

happy (and in that particular case Perl still works too because McAfee?

Guardian's LSP actually plays some 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 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 -DDEBUGGING,

this controls the behavior of global destruction of objects and other

references. See PERL_DESTRUCT_LEVEL in the perlhack manpage 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 the perlsec manpage 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 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 the perlsec manpage for more information.

Do not disclose the hash seed to people who don't need to know it.

See also hash_seed() of the Hash::Util manpage.

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

the perlvms manpage 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 the perlipc manpage.

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 the perllocale manpage. Apart from these, Perl uses no other environment variables, except to make them available to the program being executed, and to child processes. 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)};

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NAME

SYNOPSIS

DESCRIPTION

#! and quoting on non-Unix systems

Location of Perl

Command Switches

ENVIRONMENT