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NAME    [Toc]    [Back]

       perlrun - how to execute the Perl interpreter

SYNOPSIS    [Toc]    [Back]

       perl [ -sTtuUWX ]      [ -hv ] [ -V[:configvar] ]
            [ -cw ] [ -d[:debugger] ] [ -D[number/list] ]
            [  -pna  ]  [   -Fpattern   ]   [   -l[octal]   ]   [
-0[octal/hexadecimal] ]
            [ -Idir ] [ -m[-]module ] [ -M[-]'module...' ]
            [ -P ]      [ -S ]      [ -x[dir] ]
            [ -i[extension] ]
            [  -e  'command'  ] [ -- ] [ programfile ] [ argument
            [ -C [number/list] ] ]>

DESCRIPTION    [Toc]    [Back]

       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 switches on the command

       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
       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{ $/ = " digits";

       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

       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 partway
 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:


               extproc perl -S -your_switches

           as the first line in "*.cmd" file (-S due to a bug in
           cmd.exe's `extproc' handling).

           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).

           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.

           A Macintosh perl program will have the appropriate
           Creator and Type, so that double-clicking them will
           invoke the perl application.

       VMS Put

               $ perl -mysw 'f$env("procedure")' 'p1'  'p2'  'p3'
'p4' 'p5' 'p6' 'p7' 'p8' !
               $  exit++  +  ++$status != 0 and $exit = $status =

           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

           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
       ("*", "
       pace and these characters to run one-liners (see -e
       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 world0'

           # MS-DOS, etc.
           perl -e "print

           # Macintosh
           print "Hello world0
            (then Run "Myscript" or Shift-Command-R)

           # VMS
           perl -e "print ""Hello world0""

       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

           perl -e "print <Ctrl-x>"Hello world0Ctrl-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

       Location of Perl    [Toc]    [Back]

       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.

       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    [Toc]    [Back]

       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:

            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), "0;'

            is equivalent to

                while (<>) {
                    @F = split(' ');
                    print pop(@F), "0;

            An alternate delimiter may be specified using -F.
       -C [number/list]
            The "-C" flag controls some Unicode of the Perl Unicode

            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 bin-
            mode() 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 perlfunc), the twoarg
 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 Unicodeaware
 "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   runs the program under the Perl debugger.  See

            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.  See perldebug.

            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
              2097152  C  Copy On Write

            All these flags require -DDEBUGGING when you compile
            the Perl executable (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 "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.
            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.

            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

            which is equivalent to

                $extension = '.orig';
                LINE: while (<>) {
                    if ($ARGV ne $oldargv) {
                        if ($extension !~ /) {
                            $backup = $ARGV . $extension;
                        else {
                            ($backup = $extension) =~ s/$ARGV/g;
                        rename($ARGV, $backup);
                        open(ARGVOUT, ">$ARGV");
                        $oldargv = $ARGV;
                continue {
                    print;  # this prints to original filename

            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
                $ 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 readonly
 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...

            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.

            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.

            enables automatic line-ending processing.  It has two
            separate effects.  First, it automatically chomps $/
            (the input record separator) when used with -n or -p.
            Second, it assigns "$
            to have the value of octnum so that any print statements
 will have that separator added back on.  If
            octnum is omitted, sets "$
            $/.  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 "$
            null character.

       -M[-]'module ...'
            -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:

                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 modifed 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:

                while (<>) {
                    ...             # your program goes here
                } continue {
                    print or die "-p destination: $!0;

            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

       -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:

            *         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 anything 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 common
                      Perl constructs like


                      because after -P this will became illegal


                      The workaround is to use some other quoting
                      separator than "/", like for example "!":

            *         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 --).
            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 ($xyz) { print "$xyz0 }

            Do note that --help creates the variable ${-help},
            which is not compliant with "strict refs".

       -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 #!.  This example works on
            many platforms that have a shell compatible with
            Bourne shell:

                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
                    & 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 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 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 B
            and B::Bytecode 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 gen-
            erate 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.

            Prints to STDOUT the value of the named configuration
            variable(s), with multiples when your query looks
            like a regex.  For example,

                $ perl -V:lib.
                    libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';
                $ perl -V:lib.*
                    libpth='/usr/local/lib /lib /usr/lib';
                    libs='-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc';

            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
                $ echo "goodvfork="`./perl -Ilib -V::usevfork`

            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
            doesn'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 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 perllexwarn.

       -X   Disables all warnings regardless of "use warnings" or
            $^W.  See perllexwarn.

       -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).

ENVIRONMENT    [Toc]    [Back]

       HOME        Used if chdir has no argument.
       LOGDIR      Used if chdir has no argument and HOME is not

       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

                   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

                   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 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 ":perlio:bytes".

                   :crlf   A layer which does CRLF to "0 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

                   :raw    A pseudolayer that manipulates other
                           layers.  Applying the ":raw" layer is
                           equivalent  to calling "binmode($fh)".
                           It makes the stream pass each byte asis
 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

                   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" implementation if system's
                   library provides for fast access to the
                   buffer, otherwise it uses the "unix perlio"

                   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
                   "0 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 routines. There is an
                   experimental native "win32" layer which is
                   expected to be enhanced and should eventually
                   be the default under Win32.

                   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 ...

       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' }

       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).

                   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.

                   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 perlhack for more information.

                   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.

                   If using the "encoding" pragma without an
                   explicit encoding name, the PERL_ENCODING
                   environment variable is consulted for an
                   encoding name.

                   (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 nonnumeric
 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    [Toc]    [Back]
                   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

                   (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

                   Note that the hash seed is sensitive informa-    [Toc]    [Back]
                   tion: by knowing it one can craft a denial-ofservice
 attack against Perl code, even
                   remotely, see "Algorithmic Complexity Attacks"
                   in perlsec for more information.  Do not dis-
                   close the hash seed to people who don't need
                   to know it.  See also hash_seed() of

       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,
                   but are optional and discussed further in perlvms
 and in README.vms in the Perl source distribution.

                   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 perlipc.

                   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.

       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
           $ENV{SHELL} = '/bin/sh' if exists $ENV{SHELL};
           delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};

perl v5.8.5                 2002-11-06                         24
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