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PERLRUN(1)	       Perl Programmers Reference Guide 	    PERLRUN(1)

       perlrun - how to execute the Perl interpreter

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

       The normal way to run a Perl program is by making it directly exe
       cutable, or else by passing the name of the source file as an argument
       on the command line.  (An interactive Perl environment is also possi
       ble--see perldebug for details on how to do that.)  Upon startup, Perl
       looks for your program in one of the following places:

       1.  Specified line by line via -e switches on the command line.

       2.  Contained in the file specified by the first filename on the com
	   mand line.  (Note that systems supporting the #! notation invoke
	   interpreters this way. See "Location of Perl".)

       3.  Passed in implicitly via standard input.  This works only if there
	   are no filename arguments--to pass arguments to a STDIN-read pro
	   gram you must explicitly specify a "-" for the program name.

       With methods 2 and 3, Perl starts parsing the input file from the
       beginning, unless youve specified a -x switch, in which case it scans
       for the first line starting with #! and containing the word "perl", and
       starts there instead.  This is useful for running a program embedded in
       a larger message.  (In this case you would indicate the end of the pro
       gram using the "__END__" token.)

       The #! line is always examined for switches as the line is being
       parsed.	Thus, if youre on a machine that allows only one argument
       with the #! line, or worse, doesnt 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 youre not careful.  You probably want to
       make sure that all your switches fall either before or after that
       32-character boundary.  Most switches dont actually care if theyre
       processed redundantly, but getting a "-" instead of a complete switch
       could cause Perl to try to execute standard input instead of your pro
       gram.  And a partial -I switch could also cause odd results.

       Some switches do care if they are processed twice, for instance combi
       nations of -l and -0.  Either put all the switches after the 32-charac
       ter boundary (if applicable), or replace the use of -0digits by "BEGIN{
       $/ = "\0digits"; }".

       Parsing of the #! switches starts wherever "perl" is mentioned in the
       line.  The sequences "-*" and "- " are specifically ignored so that you
       could, if you were so inclined, say

	   #!/bin/sh -- # -*- perl -*- -p
	   eval exec perl -wS $0 ${1+"$@"}
	       if $running_under_some_shell;

       to let Perl see the -p switch.

       A similar trick involves the env program, if you have it.

	   #!/usr/bin/env perl

       The examples above use a relative path to the perl interpreter, getting
       whatever version is first in the users path.  If you want a specific
       version of Perl, say, perl5.005_57, you should place that directly in
       the #! lines 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 dont 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 part-way through before finding a syntax error.)

       If the program is syntactically correct, it is executed.  If the pro
       gram runs off the end without hitting an exit() or die() operator, an
       implicit exit(0) is provided to indicate successful completion.

       #! and quoting on non-Unix systems

       Unixs #! 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.exes
	   extproc handling).

	   Create a batch file to run your program, and codify it in "ALTER
	   NATE_SHEBANG" (see the dosish.h file in the source distribution for
	   more information).

	   The Win95/NT installation, when using the ActiveState installer for
	   Perl, will modify the Registry to associate the .pl extension with
	   the perl interpreter.  If you install Perl by other means (includ
	   ing building from the sources), you may have to modify the Registry
	   yourself.  Note that this means you can no longer tell the differ
	   ence between an executable Perl program and a Perl library file.

	   Under "Classic" MacOS, a perl program will have the appropriate
	   Creator and Type, so that double-clicking them will invoke the
	   MacPerl application.  Under Mac OS X, clickable apps can be made
	   from any "#!" script using Wil Sanchez DropScript utility:
	   http://www.wsanchez.net/software/ .

       VMS Put

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

	   at the top of your program, where -mysw are any command line
	   switches you want to pass to Perl.  You can now invoke the program
	   directly, by saying "perl program", or as a DCL procedure, by say
	   ing @program (or implicitly via DCL$PATH by just using the name of
	   the program).

	   This incantation is a bit much to remember, but Perl will display
	   it for you if you say "perl "-V:startperl"".

       Command-interpreters on non-Unix systems have rather different ideas on
       quoting than Unix shells.  Youll 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

       On some systems, you may have to change single-quotes to double ones,
       which you must not do on Unix or Plan 9 systems.  You might also have
       to change a single % to a %%.

       For example:

	   # Unix
	   perl -e print "Hello world\n"

	   # MS-DOS, etc.
	   perl -e "print \"Hello world\n\""

	   # Macintosh
	   print "Hello world\n"
	    (then Run "Myscript" or Shift-Command-R)

	   # VMS
	   perl -e "print ""Hello world\n"""

       The problem is that none of this is reliable: it depends on the command
       and it is entirely possible neither works.  If 4DOS were the command
       shell, this would probably work better:

	   perl -e "print "Hello world\n""

       CMD.EXE in Windows NT slipped a lot of standard Unix functionality in
       when nobody was looking, but just try to find documentation for its
       quoting rules.

       Under the Macintosh, it depends which environment you are using.  The
       MacPerl shell, or MPW, is much like Unix shells in its support for sev
       eral quoting variants, except that it makes free use of the Macintoshs
       non-ASCII characters as control characters.

       There is no general solution to all of this.  Its just a mess.

       Location of Perl

       It may seem obvious to say, but Perl is useful only when users can eas
       ily find it.  When possible, its good for both /usr/bin/perl and
       /usr/local/bin/perl to be symlinks to the actual binary.  If that cant
       be done, system administrators are strongly encouraged to put (symlinks
       to) perl and its accompanying utilities into a directory typically
       found along a users PATH, or in some other obvious and convenient

       In this documentation, "#!/usr/bin/perl" on the first line of the pro
       gram will stand in for whatever method works on your system.  You are
       advised to use a specific path if you care about a specific version.


       or if you just want to be running at least version, place a statement
       like this at the top of your program:

	   use 5.005_54;

       Command Switches

       As with all standard commands, a single-character switch may be clus
       tered with the following switch, if any.

	   #!/usr/bin/perl -spi.orig   # same as -s -p -i.orig

       Switches include:

	    specifies the input record separator ($/) as an octal or hexadeci
	    mal number.  If there are no digits, the null character is the
	    separator.	Other switches may precede or follow the digits.  For
	    example, if you have a version of find which can print filenames
	    terminated by the null character, you can say this:

		find . -name *.orig -print0 | perl -n0e unlink

	    The special value 00 will cause Perl to slurp files in paragraph
	    mode.  The value 0777 will cause Perl to slurp files whole because
	    there is no legal byte with that value.

	    If you want to specify any Unicode character, use the hexadecimal
	    format: "-0xHHH...", where the "H" are valid hexadecimal digits.
	    (This means that you cannot use the "-x" with a directory name
	    that consists of hexadecimal digits.)

       -a   turns on autosplit mode when used with a -n or -p.	An implicit
	    split command to the @F array is done as the first thing inside
	    the implicit while loop produced by the -n or -p.

		perl -ane print pop(@F), "\n";

	    is equivalent to

		while (<>) {
		    @F = split( );
		    print pop(@F), "\n";

	    An alternate delimiter may be specified using -F.

       -C [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 num

		I     1    STDIN is assumed to be in UTF-8
		O     2    STDOUT will be in UTF-8
		E     4    STDERR will be in UTF-8
		S     7    I + O + E
		i     8    UTF-8 is the default PerlIO layer for input streams
		o    16    UTF-8 is the default PerlIO layer for output streams
		D    24    i + o
		A    32    the @ARGV elements are expected to be strings encoded in UTF-8
		L    64    normally the "IOEioA" are unconditional,
			   the L makes them conditional on the locale environment
			   variables (the LC_ALL, LC_TYPE, and LANG, in the order
			   of decreasing precedence) -- if the variables indicate
			   UTF-8, then the selected "IOEioA" are in effect

	    For example, "-COE" and "-C6" will both turn on UTF-8-ness on both
	    STDOUT and STDERR.	Repeating letters is just redundant, not cumu
	    lative nor toggling.

	    The "io" options mean that any subsequent open() (or similar I/O
	    operations) will have the ":utf8" PerlIO layer implicitly applied
	    to them, in other words, UTF-8 is expected from any input stream,
	    and UTF-8 is produced to any output stream.  This is just the
	    default, with explicit layers in open() and with binmode() one can
	    manipulate streams as usual.

	    "-C" on its own (not followed by any number or option list), or
	    the empty string "" for the "PERL_UNICODE" environment variable,
	    has the same effect as "-CSDL".  In other words, the standard I/O
	    handles and the default "open()" layer are UTF-8-fied but only if
	    the locale environment variables indicate a UTF-8 locale.  This
	    behaviour follows the implicit (and problematic) UTF-8 behaviour
	    of Perl 5.8.0.

	    You can use "-C0" (or "0" for "PERL_UNICODE") to explicitly dis
	    able all the above Unicode features.

	    The read-only magic variable "${^UNICODE}" reflects the numeric
	    value of this setting.  This is variable is set during Perl
	    startup and is thereafter read-only.  If you want runtime effects,
	    use the three-arg open() (see "open" in perlfunc), the two-arg
	    binmode() (see "binmode" in perlfunc), and the "open" pragma (see

	    (In Perls earlier than 5.8.1 the "-C" switch was a Win32-only
	    switch that enabled the use of Unicode-aware "wide system call"
	    Win32 APIs.  This feature was practically unused, however, and the
	    command line switch was therefore "recycled".)

       -c   causes Perl to check the syntax of the program and then exit with
	    out executing it.  Actually, it will execute "BEGIN", "CHECK", and
	    "use" blocks, because these are considered as occurring outside
	    the execution of your program.  "INIT" and "END" blocks, however,
	    will be skipped.

       -dt  runs the program under the Perl debugger.  See perldebug.  If t is
	    specified, it indicates to the debugger that threads will be used
	    in the code being debugged.

	    runs the program under the control of a debugging, profiling, or
	    tracing module installed as Devel::foo. E.g., -d:DProf executes
	    the program using the Devel::DProf profiler.  As with the -M flag,
	    options may be passed to the Devel::foo package where they will be
	    received and interpreted by the Devel::foo::import routine.  The
	    comma-separated list of options must follow a "=" character.  If t
	    is specified, it indicates to the debugger that threads will be
	    used in the code being debugged.  See perldebug.

	    sets debugging flags.  To watch how it executes your program, use
	    -Dtls.  (This works only if debugging is compiled into your Perl.)
	    Another nice value is -Dx, which lists your compiled syntax tree.
	    And -Dr displays compiled regular expressions; the format of the
	    output is explained in perldebguts.

	    As an alternative, specify a number instead of list of letters
	    (e.g., -D14 is equivalent to -Dtls):

		    1  p  Tokenizing and parsing
		    2  s  Stack snapshots (with v, displays all stacks)
		    4  l  Context (loop) stack processing
		    8  t  Trace execution
		   16  o  Method and overloading resolution
		   32  c  String/numeric conversions
		   64  P  Print profiling info, preprocessor command for -P, source file input state
		  128  m  Memory allocation
		  256  f  Format processing
		  512  r  Regular expression parsing and execution
		 1024  x  Syntax tree dump
		 2048  u  Tainting checks
		 4096	  (Obsolete, previously used for LEAKTEST)
		 8192  H  Hash dump -- usurps values()
		16384  X  Scratchpad allocation
		32768  D  Cleaning up
		65536  S  Thread synchronization
	       131072  T  Tokenising
	       262144  R  Include reference counts of dumped variables (eg when using -Ds)
	       524288  J  Do not s,t,P-debug (Jump over) opcodes within package DB
	      1048576  v  Verbose: use in conjunction with other flags
	      8388608  q  quiet - currently only suppresses the "EXECUTING" message

	    All these flags require -DDEBUGGING when you compile the Perl exe
	    cutable (but see Devel::Peek, re which may change this).  See the
	    INSTALL file in the Perl source distribution for how to do this.
	    This flag is automatically set if you include -g option when "Con
	    figure" asks you about optimizer/debugger flags.

	    If youre 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 cant use Perls -D switch.  Instead do this

	      # If you have "env" utility
	      env PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

	      # Bourne shell syntax
	      $ PERLDB_OPTS="NonStop=1 AutoTrace=1 frame=2" perl -dS program

	      # csh syntax
	      % (setenv PERLDB_OPTS "NonStop=1 AutoTrace=1 frame=2"; perl -dS program)

	    See perldebug for details and variations.

       -e commandline
	    may be used to enter one line of program.  If -e is given, Perl
	    will not look for a filename in the argument list.	Multiple -e
	    commands may be given to build up a multi-line script.  Make sure
	    to use semicolons where you would in a normal program.

       -f   Disable executing $Config{sitelib}/sitecustomize.pl at startup.

	    Perl can be built so that it by default will try to execute $Con
	    fig{sitelib}/sitecustomize.pl at startup.  This is a hook that
	    allows the sysadmin to customize how perl behaves.	It can for
	    instance be used to add entries to the @INC array to make perl
	    find modules in non-standard locations.

	    specifies the pattern to split on if -a is also in effect.	The
	    pattern may be surrounded by "//", "", or , otherwise it will be
	    put in single quotes. You cant use literal whitespace in the pat

       -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 doesnt 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 -piorig_* -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 -piold/*.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 doesnt 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

		$ 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 perlfunc).

	    If, for a given file, Perl is unable to create the backup file as
	    specified in the extension then it will skip that file and con
	    tinue on with the next one (if it exists).

	    For a discussion of issues surrounding file permissions and -i,
	    see "Why does Perl let me delete read-only files? Why does -i
	    clobber protected files? Isnt this a bug in Perl?" in perlfaq5.

	    You cannot use -i to create directories or to strip extensions
	    from files.

	    Perl does not expand "~" in filenames, which is good, since some
	    folks use it for their backup files:

		$ perl -pi~ -e s/foo/bar/ file1 file2 file3...

	    Note that because -i renames or deletes the original file before
	    creating a new file of the same name, UNIX-style soft and hard
	    links will not be preserved.

	    Finally, the -i switch does not impede execution when no files are
	    given on the command line.	In this case, no backup is made (the
	    original file cannot, of course, be determined) and processing
	    proceeds from STDIN to STDOUT as might be expected.

	    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 $/ (the input record sep
	    arator) when used with -n or -p.  Second, it assigns "$\" (the
	    output record separator) to have the value of octnum so that any
	    print statements will have that separator added back on.  If oct
	    num is omitted, sets "$\" to the current value of $/.  For
	    instance, to trim lines to 80 columns:

		perl -lpe substr($_, 80) = ""

	    Note that the assignment "$\ = $/" is done when the switch is
	    processed, so the input record separator can be different than the
	    output record separator if the -l switch is followed by a -0

		gnufind / -print0 | perl -ln0e print "found $_" if -p

	    This sets "$\" to newline and then sets $/ to the null character.

       -M[-]module ...
	    -mmodule executes "use" module "();" before executing your pro

	    -Mmodule executes "use" module ";" before executing your program.
	    You can use quotes to add extra code after the module name, e.g.,
	    -Mmodule qw(foo bar).

	    If the first character after the -M or -m is a dash ("-") then the
	    use is replaced with no.

	    A little builtin syntactic sugar means you can also say -mmod
	    ule=foo,bar or -Mmodule=foo,bar as a shortcut for -Mmodule qw(foo
	    bar).  This avoids the need to use quotes when importing symbols.
	    The actual code generated by -Mmodule=foo,bar is "use module
	    split(/,/,q{foo,bar})".  Note that the "=" form removes the dis
	    tinction between -m and -M.

	    A consequence of this is that -MFoo=number never does a version
	    check (unless "Foo::import()" itself is set up to do a version
	    check, which could happen for example if Foo inherits from

       -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

	    Here is an efficient way to delete all files that havent 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
	    dont 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: $!\n";

	    If a file named by an argument cannot be opened for some reason,
	    Perl warns you about it, and moves on to the next file.  Note that
	    the lines are printed automatically.  An error occurring during
	    printing is treated as fatal.  To suppress printing use the -n
	    switch.  A -p overrides a -n switch.

	    "BEGIN" and "END" blocks may be used to capture control before or
	    after the implicit loop, just as in awk.

       -P   NOTE: Use of -P is strongly discouraged because of its inherent
	    problems, including poor portability.

	    This option causes your program to be run through the C preproces
	    sor before compilation by Perl.  Because both comments and cpp
	    directives begin with the # character, you should avoid starting
	    comments with any words recognized by the C preprocessor such as
	    "if", "else", or "define".

	    If youre 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 dont

	    *	      A "-P" on a "#!" line doesnt work.

	    *	      All lines that begin with (whitespace and) a "#" but do
		      not look like cpp commands, are stripped, including any
		      thing inside Perl strings, regular expressions, and
		      here-docs .

	    *	      In some platforms the C preprocessor knows too much: it
		      knows about the C++ -style until-end-of-line comments
		      starting with "//".  This will cause problems with com
		      mon Perl constructs like


		      because after -P this will became illegal code


		      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 --).	Any switch found there is removed from
	    @ARGV and sets the corresponding variable in the Perl program.
	    The following program prints "1" if the program is invoked with a
	    -xyz switch, and "abc" if it is invoked with -xyz=abc.

		#!/usr/bin/perl -s
		if ($xyz) { print "$xyz\n" }

	    Do note that a switch like --help creates the variable ${-help},
	    which is not compliant with "strict refs".	Also, when using this
	    option on a script with warnings enabled you may get a lot of spu
	    rious "used only once" warnings.

       -S   makes Perl use the PATH environment variable to search for the
	    program (unless the name of the program contains directory separa

	    On some platforms, this also makes Perl append suffixes to the
	    filename while searching for it.  For example, on Win32 platforms,
	    the ".bat" and ".cmd" suffixes are appended if a lookup for the
	    original name fails, and if the name does not already end in one
	    of those suffixes.	If your Perl was compiled with DEBUGGING
	    turned on, using the -Dp switch to Perl shows how the search pro

	    Typically this is used to emulate #! startup on platforms that
	    dont support #!.  Its also convenient when debugging a script
	    that uses #!, and is thus normally found by the shells $PATH
	    search mechanism.

	    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 doesnt always contain the full pathname, so the -S
	    tells Perl to search for the program if necessary.	After Perl
	    locates the program, it parses the lines and ignores them because
	    the variable $running_under_some_shell is never true.  If the pro
	    gram will be interpreted by csh, you will need to replace
	    "${1+"$@"}" with $*, even though that doesnt 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 cant control that, and need a totally devious con
	    struct that will work under any of csh, sh, or Perl, such as the

		    eval (exit $?0) && eval exec perl -wS $0 ${1+"$@"}
		    & eval exec /usr/bin/perl -wS $0 $argv:q
			    if $running_under_some_shell;

	    If the filename supplied contains directory separators (i.e., is
	    an absolute or relative pathname), and if that file is not found,
	    platforms that append file extensions will do so and try to look
	    for the file with those extensions added, one by one.

	    On DOS-like platforms, if the program does not contain directory
	    separators, it will first be searched for in the current directory
	    before being searched for on the PATH.  On Unix platforms, the
	    program will be searched for strictly on the PATH.

       -t   Like -T, but taint checks will issue warnings rather than fatal
	    errors.  These warnings can be controlled normally with "no warn
	    ings qw(taint)".

	    NOTE: this is not a substitute for -T. This is meant only to be
	    used as a temporary development aid while securing legacy code:
	    for real production code and for new secure code written from
	    scratch always use the real -T.

       -T   forces "taint" checks to be turned on so you can test them.  Ordi
	    narily these checks are done only when running setuid or setgid.
	    Its a good idea to turn them on explicitly for programs that run
	    on behalf of someone else whom you might not necessarily trust,
	    such as CGI programs or any internet servers you might write in
	    Perl.  See perlsec for details.  For security reasons, this option
	    must be seen by Perl quite early; usually this means it must
	    appear early on the command line or in the #! line for systems
	    which support that construct.

       -u   This obsolete switch causes Perl to dump core after compiling your
	    program.  You can then in theory take this core dump and turn it
	    into an executable file by using the undump program (not sup
	    plied).  This speeds startup at the expense of some disk space
	    (which you can minimize by stripping the executable).  (Still, a
	    "hello world" executable comes out to about 200K on my machine.)
	    If you want to execute a portion of your program before dumping,
	    use the dump() operator instead.  Note: availability of undump is
	    platform specific and may not be available for a specific port of

	    This switch has been superseded in favor of the new Perl code gen
	    erator backends to the compiler.  See B and B::Bytecode for

       -U   allows Perl to do unsafe operations.  Currently the only "unsafe"
	    operations are attempting to unlink directories while running as
	    superuser, and running setuid programs with fatal taint checks
	    turned into warnings.  Note that the -w switch (or the $^W vari
	    able) must be used along with this option to actually generate the
	    taint-check warnings.

       -v   prints the version and patchlevel of your perl executable.

       -V   prints summary of the major perl configuration values and the cur
	    rent values of @INC.

	    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
		$ 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 ;, allow
	    ing you to embed queries into shell commands.  (mnemonic: PATH
	    separator :.)

		$ echo "compression-vars: " perl -V:z.*:  " are here !"
		compression-vars:  zcat= zip=zip  are here !

	    A leading colon removes the name= part of the response, this
	    allows you to map to the name you need.  (mnemonic: empty label)

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

	    Leading and trailing colons can be used together if you need posi
	    tional parameter values without the names.	Note that in the case
	    below, the PERL_API params are returned in alphabetical order.

		$ echo building_on perl -V::osname: -V::PERL_API_.*: now
		building_on linux 5 1 9 now

       -w   prints warnings about dubious constructs, such as variable names
	    that are mentioned only once and scalar variables that are used
	    before being set, redefined subroutines, references to undefined
	    filehandles or filehandles opened read-only that you are attempt
	    ing to write on, values used as a number that dont look like num
	    bers, using an array as though it were a scalar, if your subrou
	    tines recurse more than 100 deep, and innumerable other things.

	    This switch really just enables the internal $^W variable.	You
	    can disable or promote into fatal errors specific warnings using
	    "__WARN__" hooks, as described in perlvar and "warn" in perlfunc.
	    See also perldiag and perltrap.  A new, fine-grained warning
	    facility is also available if you want to manipulate entire
	    classes of warnings; see warnings or perllexwarn.

       -W   Enables all warnings regardless of "no warnings" or $^W.  See per

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

       -x directory
	    tells Perl that the program is embedded in a larger chunk of unre
	    lated ASCII text, such as in a mail message.  Leading garbage will
	    be discarded until the first line that starts with #! and contains
	    the string "perl".	Any meaningful switches on that line will be
	    applied.  If a directory name is specified, Perl will switch to
	    that directory before running the program.	The -x switch controls
	    only the disposal of leading garbage.  The program must be termi
	    nated with "__END__" if there is trailing garbage to be ignored
	    (the program can process any or all of the trailing garbage via
	    the DATA filehandle if desired).

       HOME	   Used if chdir has no argument.

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

       PATH	   Used in executing subprocesses, and in finding the program
		   if -S is used.

       PERL5LIB    A list of directories in which to look for Perl library
		   files before looking in the standard library and the cur
		   rent directory.  Any architecture-specific directories
		   under the specified locations are automatically included if
		   they exist.	If PERL5LIB is not defined, PERLLIB is used.
		   Directories are separated (like in PATH) by a colon on
		   unixish platforms and by a semicolon on Windows (the proper
		   path separator being given by the command "perl

		   When running taint checks (either because the program was
		   running setuid or setgid, or the -T switch was used), nei
		   ther variable is used.  The program should instead say:

		       use lib "/my/directory";

       PERL5OPT    Command-line options (switches).  Switches in this variable
		   are taken as if they were on every Perl command line.  Only
		   the -[DIMUdmtw] switches are allowed.  When running taint
		   checks (because the program was running setuid or setgid,
		   or the -T switch was used), this variable is ignored.  If
		   PERL5OPT begins with -T, tainting will be enabled, and any
		   subsequent options ignored.

       PERLIO	   A space (or colon) separated list of PerlIO layers. If perl
		   is built to use PerlIO system for IO (the default) these
		   layers effect perls IO.

		   It is conventional to start layer names with a colon e.g.
		   ":perlio" to emphasise their similarity to variable
		   "attributes". But the code that parses layer specification
		   strings (which is also used to decode the PERLIO environ
		   ment variable) treats the colon as a separator.

		   An unset or empty PERLIO is equivalent to ":stdio".

		   The list becomes the default for all perls IO. Conse
		   quently only built-in layers can appear in this list, as
		   external layers (such as :encoding()) need IO in  order to
		   load them!. See "open pragma" for how to add external
		   encodings as defaults.

		   The layers that it makes sense to include in the PERLIO
		   environment variable are briefly summarised below. For more
		   details see PerlIO.

		   :bytes  A pseudolayer that turns off the ":utf8" flag for
			   the layer below.  Unlikely to be useful on its own
			   in the global PERLIO environment variable.  You
			   perhaps were thinking of ":crlf:bytes" or ":per

		   :crlf   A layer which does CRLF to "\n" translation distin
			   guishing "text" and "binary" files in the manner of
			   MS-DOS and similar operating systems.  (It cur
			   rently does not mimic MS-DOS as far as treating of
			   Control-Z as being an end-of-file marker.)

		   :mmap   A layer which implements "reading" of files by
			   using "mmap()" to make (whole) file appear in the
			   processs address space, and then using that as
			   PerlIOs "buffer".

		   :perlio This is a re-implementation of "stdio-like" buffer
			   ing written as a PerlIO "layer".  As such it will
			   call whatever layer is below it for its operations
			   (typically ":unix").

		   :pop    An experimental pseudolayer that removes the top
			   most layer.	Use with the same care as is reserved
			   for nitroglycerin.

		   :raw    A pseudolayer that manipulates other layers.
			   Applying the ":raw" layer is equivalent to calling
			   "binmode($fh)".  It makes the stream pass each byte
			   as-is without any translation.  In particular CRLF
			   translation, and/or :utf8 intuited from locale are

			   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
			   systems 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" implementa
		   tion if systems library provides for fast access to the
		   buffer, otherwise it uses the "unix perlio" implementation.

		   On Win32 the default in this release is "unix crlf".
		   Win32s "stdio" has a number of bugs/mis-features for perl
		   IO which are somewhat C compiler vendor/version dependent.
		   Using our own "crlf" layer as the buffer avoids those
		   issues and makes things more uniform.  The "crlf" layer
		   provides CRLF to/from "\n" conversion as well as buffering.

		   This release uses "unix" as the bottom layer on Win32 and
		   so still uses C compilers numeric file descriptor rou
		   tines. There is an experimental native "win32" layer which
		   is expected to be enhanced and should eventually be the
		   default under Win32.

		   If set to the name of a file or device then certain opera
		   tions of PerlIO sub-system will be logged to that file
		   (opened as append). Typical uses are UNIX:

		      PERLIO_DEBUG=/dev/tty perl script ...

		   and Win32 approximate equivalent:

		      set PERLIO_DEBUG=CON
		      perl script ...

		   This functionality is disabled for setuid scripts and for
		   scripts run with -T.

       PERLLIB	   A list of directories in which to look for Perl library
		   files before looking in the standard library and the
		   current directory.  If PERL5LIB is defined, PERLLIB is not

       PERL5DB	   The command used to load the debugger code.	The default

			   BEGIN { require perl5db.pl }

		   If set to a true value, indicates to the debugger that the
		   code being debugged uses threads.

       PERL5SHELL (specific to the Win32 port)
		   May be set to an alternative shell that perl must use
		   internally for executing "backtick" commands or system().
		   Default is "cmd.exe /x/d/c" on WindowsNT and "command.com
		   /c" on Windows95.  The value is considered to be space-sep
		   arated.  Precede any character that needs to be protected
		   (like a space or backslash) with a backslash.

		   Note that Perl doesnt use COMSPEC for this purpose because
		   COMSPEC has a high degree of variability among users, lead
		   ing to portability concerns.  Besides, perl can use a shell
		   that may not be fit for interactive use, and setting COM
		   SPEC to such a shell may interfere with the proper func
		   tioning of other programs (which usually look in COMSPEC to
		   find a shell fit for interactive use).

       PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
		   Set to 1 to allow the use of non-IFS compatible LSPs.
		   Perl normally searches for an IFS-compatible LSP because
		   this is required for its emulation of Windows sockets as
		   real filehandles.  However, this may cause problems if you
		   have a firewall such as McAfee Guardian which requires all
		   applications to use its LSP which is not IFS-compatible,
		   because clearly Perl will normally avoid using such an LSP.
		   Setting this environment variable to 1 means that Perl will
		   simply use the first suitable LSP enumerated in the cata
		   log, which keeps McAfee Guardian happy (and in that partic
		   ular case Perl still works too because McAfee Guardians
		   LSP actually plays some other games which allow applica
		   tions requiring IFS compatibility to work).

		   Relevant only if perl is compiled with the malloc included
		   with the perl distribution (that is, if "perl -V:d_mymal
		   loc" is define).  If set, this causes memory statistics
		   to be dumped after execution.  If set to an integer greater
		   than one, also causes memory statistics to be dumped after

		   Relevant only if your perl executable was built with -DDE
		   BUGGING, this controls the behavior of global destruction
		   of objects and other references.  See "PERL_DESTRUCT_LEVEL"
		   in perlhack for more information.

		   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 doesnt 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 Perls internal hash
		   function.  To emulate the pre-5.8.1 behaviour, set to an
		   integer (zero means exactly the same order as 5.8.0).
		   "Pre-5.8.1" means, among other things, that hash keys will
		   be ordered the same between different runs of Perl.

		   The default behaviour is to randomise unless the
		   PERL_HASH_SEED is set.  If Perl has been compiled with
		   "-DUSE_HASH_SEED_EXPLICIT", the default behaviour is not to
		   randomise unless the PERL_HASH_SEED is set.

		   If PERL_HASH_SEED is unset or set to a non-numeric string,
		   Perl uses the pseudorandom seed supplied by the operating
		   system and libraries.  This means that each different run
		   of Perl will have a different ordering of the results of
		   keys(), values(), and each().

		   Please note that the hash seed is sensitive information.
		   Hashes are randomized to protect against local and remote
		   attacks against Perl code. By manually setting a seed this
		   protection may be partially or completely lost.

		   See "Algorithmic Complexity Attacks" in perlsec and
		   "PERL_HASH_SEED_DEBUG" for more information.

		   (Since Perl 5.8.1.)	Set to one to display (to STDERR) the
		   value of the hash seed at the beginning of execution.
		   This, combined with "PERL_HASH_SEED" is intended to aid in
		   debugging nondeterministic behavior caused by hash random

		   Note that the hash seed is sensitive information: by know
		   ing it one can craft a denial-of-service attack against
		   Perl code, even remotely, see "Algorithmic Complexity
		   Attacks" in perlsec for more information.  Do not disclose
		   the hash seed to people who dont need to know it.  See
		   also hash_seed() of Hash::Util.

       PERL_ROOT (specific to the VMS port)
		   A translation concealed rooted logical name that contains
		   perl and the logical device for the @INC path on VMS only.
		   Other logical names that affect perl on VMS include PERL
		   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 per

		   Equivalent to the -C command-line switch.  Note that this
		   is not a boolean variable-- setting this to "1" is not the
		   right way to "enable Unicode" (whatever that would mean).
		   You can use "0" to "disable Unicode", though (or alterna
		   tively unset PERL_UNICODE in your shell before starting
		   Perl).  See the description of the "-C" switch for more

       SYS$LOGIN (specific to the VMS port)
		   Used if chdir has no argument and HOME and LOGDIR are not

       Perl also has environment variables that control how Perl handles data
       specific to particular natural languages.  See perllocale.

       Apart from these, Perl uses no other environment variables, except to
       make them available to the program being executed, and to child pro
       cesses.	However, programs running setuid would do well to execute the
       following lines before doing anything else, just to keep people honest:

	   $ENV{PATH}  = /bin:/usr/bin;    # or whatever you need
	   $ENV{SHELL} = /bin/sh if exists $ENV{SHELL};
	   delete @ENV{qw(IFS CDPATH ENV BASH_ENV)};

perl v5.8.8			  2008-04-25			    PERLRUN(1)

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