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

       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] ]      [ -S ]	  [ -x[dir] ]
	    [ -i[extension] ]
	    [ [-e|-E] 'command' ] [ -- ] [ programfile ] [ argument ]...

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

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

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

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

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

       The "#!" line is always examined for switches as the line is being
       parsed.	Thus, if you're on a machine that allows only one argument
       with the "#!" line, or worse, doesn't even recognize the "#!" line, you
       still can get consistent switch behaviour regardless of how Perl was
       invoked, even if -x was used to find the beginning of the program.

       Because historically some operating systems silently chopped off kernel
       interpretation of the "#!" line after 32 characters, some switches may
       be passed in on the command line, and some may not; you could even get
       a "-" without its letter, if you're not careful.	 You probably want to
       make sure that all your switches fall either before or after that
       32-character boundary.  Most switches don't actually care if they're
       processed redundantly, but getting a "-" instead of a complete switch
       could cause Perl to try to execute standard input instead of your
       program.	 And a partial -I switch could also cause odd results.

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

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

	   #! -*-perl-*-
	   eval 'exec perl -x -wS $0 ${1+"$@"}'
	       if 0;

       to let Perl see the -p switch.

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

	   #!/usr/bin/env perl

       The examples above use a relative path to the perl interpreter, getting
       whatever version is first in the user's path.  If you want a specific
       version of Perl, say, perl5.14.1, you should place that directly in the
       "#!" line's path.

       If the "#!" line does not contain the word "perl" nor the word "indir"
       the program named after the "#!" is executed instead of the Perl
       interpreter.  This is slightly bizarre, but it helps people on machines
       that don't do "#!", because they can tell a program that their SHELL is
       /usr/bin/perl, and Perl will then dispatch the program to the correct
       interpreter for them.

       After locating your program, Perl compiles the entire program to an
       internal form.  If there are any compilation errors, execution of the
       program is not attempted.  (This is unlike the typical shell script,
       which might run part-way through before finding a syntax error.)

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

   #! and quoting on non-Unix systems
       Unix's "#!" technique can be simulated on other systems:


	       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

       VMS Put

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

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

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

       Command-interpreters on non-Unix systems have rather different ideas on
       quoting than Unix shells.  You'll need to learn the special characters
       in your command-interpreter ("*", "\" and """ are common) and how to
       protect whitespace and these characters to run one-liners (see -e

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

       For example:

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

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

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

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

	   perl -e "print <Ctrl-x>"Hello world\n<Ctrl-x>""

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

       There is no general solution to all of this.  It's just a mess.

   Location of Perl
       It may seem obvious to say, but Perl is useful only when users can
       easily find it.	When possible, it's good for both /usr/bin/perl and
       /usr/local/bin/perl to be symlinks to the actual binary.	 If that can't
       be done, system administrators are strongly encouraged to put (symlinks
       to) perl and its accompanying utilities into a directory typically
       found along a user's PATH, or in some other obvious and convenient

       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


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

	   use 5.014;

   Command Switches
       As with all standard commands, a single-character switch may be
       clustered with the following switch, if any.

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

       Switches include:

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

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

	    The special value 00 will cause Perl to slurp files in paragraph
	    mode.  Any value 0400 or above will cause Perl to slurp files
	    whole, but by convention the value 0777 is the one normally used
	    for this purpose.

	    You can also specify the separator character using hexadecimal
	    notation: -0xHHH..., where the "H" are valid hexadecimal digits.
	    Unlike the octal form, this one may be used to specify any Unicode
	    character, even those beyond 0xFF.	So if you really want a record
	    separator of 0777, specify it as -0x1FF.  (This means that you
	    cannot use the -x option with a directory name that consists of
	    hexadecimal digits, or else Perl will think you have specified a
	    hex number to -0.)

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

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

	    is equivalent to

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

	    An alternate delimiter may be specified using -F.

       -C [number/list]
	    The -C flag controls some of the Perl Unicode features.

	    As of 5.8.1, the -C can be followed either by a number or a list
	    of option letters.	The letters, their numeric values, and effects
	    are as follows; listing the letters is equal to summing the

		I     1	  STDIN is assumed to be in UTF-8
		O     2	  STDOUT will be in UTF-8
		E     4	  STDERR will be in UTF-8
		S     7	  I + O + E
		i     8	  UTF-8 is the default PerlIO layer for input streams
		o    16	  UTF-8 is the default PerlIO layer for output streams
		D    24	  i + o
		A    32	  the @ARGV elements are expected to be strings encoded
			  in UTF-8
		L    64	  normally the "IOEioA" are unconditional, the L makes
			  them conditional on the locale environment variables
			  (the LC_ALL, LC_TYPE, and LANG, in the order of
			  decreasing precedence) -- if the variables indicate
			  UTF-8, then the selected "IOEioA" are in effect
		a   256	  Set ${^UTF8CACHE} to -1, to run the UTF-8 caching
			  code in debugging mode.

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

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

	    -C on its own (not followed by any number or option list), or the
	    empty string "" for the "PERL_UNICODE" environment variable, has
	    the same effect as -CSDL.  In other words, the standard I/O
	    handles and the default "open()" layer are UTF-8-fied but only if
	    the locale environment variables indicate a UTF-8 locale.  This
	    behaviour follows the implicit (and problematic) UTF-8 behaviour
	    of Perl 5.8.0.  (See "UTF-8 no longer default under UTF-8 locales"
	    in perl581delta.)

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

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

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

	    Note: Since perl 5.10.1, if the -C option is used on the "#!"
	    line, it must be specified on the command line as well, since the
	    standard streams are already set up at this point in the execution
	    of the perl interpreter.  You can also use binmode() to set the
	    encoding of an I/O stream.

       -c   causes Perl to check the syntax of the program and then exit
	    without executing it.  Actually, it will execute and "BEGIN",
	    "UNITCHECK", or "CHECK" blocks and any "use" statements: these are
	    considered as occurring outside the execution of your program.
	    "INIT" and "END" blocks, however, will be skipped.

       -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::MOD". E.g., -d:DProf executes
	    the program using the "Devel::DProf" profiler.  As with the -M
	    flag, options may be passed to the "Devel::MOD" package where they
	    will be received and interpreted by the "Devel::MOD::import"
	    routine.  Again, like -M, use --d:-MOD to call
	    "Devel::MOD::unimport" instead of import.  The comma-separated
	    list of options must follow a "=" character.  If t is specified,
	    it indicates to the debugger that threads will be used in the code
	    being debugged.  See perldebug.

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

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

		    1  p  Tokenizing and parsing (with v, displays parse stack)
		    2  s  Stack snapshots (with v, displays all stacks)
		    4  l  Context (loop) stack processing
		    8  t  Trace execution
		   16  o  Method and overloading resolution
		   32  c  String/numeric conversions
		   64  P  Print profiling info, source file input state
		  128  m  Memory and SV allocation
		  256  f  Format processing
		  512  r  Regular expression parsing and execution
		 1024  x  Syntax tree dump
		 2048  u  Tainting checks
		 4096  U  Unofficial, User hacking (reserved for private,
			  unreleased use)
		 8192  H  Hash dump -- usurps values()
		16384  X  Scratchpad allocation
		32768  D  Cleaning up
		65536  S  Op slab allocation
	       131072  T  Tokenizing
	       262144  R  Include reference counts of dumped variables (eg when
			  using -Ds)
	       524288  J  show s,t,P-debug (don't Jump over) on opcodes within
			  package DB
	      1048576  v  Verbose: use in conjunction with other flags
	      2097152  C  Copy On Write
	      4194304  A  Consistency checks on internal structures
	      8388608  q  quiet - currently only suppresses the "EXECUTING"
	     16777216  M  trace smart match resolution
	     33554432  B  dump suBroutine definitions, including special Blocks
			  like BEGIN

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

	    If you're just trying to get a print out of each line of Perl code
	    as it executes, the way that "sh -x" provides for shell scripts,
	    you can't use Perl's -D switch.  Instead do this

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

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

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

	    See perldebug for details and variations.

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

       -E commandline
	    behaves just like -e, except that it implicitly enables all
	    optional features (in the main compilation unit). See feature.

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

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

	    Perl actually inserts the following code:

		    do { local $!; -f "$Config{sitelib}/"; }
			&& do "$Config{sitelib}/";

	    Since it is an actual "do" (not a "require"),
	    doesn't need to return a true value. The code is run in package
	    "main", in its own lexical scope. However, if the script dies, $@
	    will not be set.

	    The value of $Config{sitelib} is also determined in C code and not
	    read from "", which is not loaded.

	    The code is executed very early. For example, any changes made to
	    @INC will show up in the output of `perl -V`. Of course, "END"
	    blocks will be likewise executed very late.

	    To determine at runtime if this capability has been compiled in
	    your perl, you can check the value of $Config{usesitecustomize}.

	    specifies the pattern to split on if -a is also in effect.	The
	    pattern may be surrounded by "//", "", or '', otherwise it will be
	    put in single quotes. You can't use literal whitespace in the

       -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, and your system supports it, the
	    original file is kept open without a name while the output is
	    redirected to a new file with the original filename.  When perl
	    exits, cleanly or not, the original file is unlinked.

	    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

		$ 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
	    continue on with the next one (if it exists).

	    For a discussion of issues surrounding file permissions and -i,
	    see "Why does Perl let me delete read-only files?  Why does -i
	    clobber protected files?  Isn't this a bug in Perl?" in perlfaq5.

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

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

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

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

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

	    Directories specified by -I are prepended to the search path for
	    modules (@INC).

	    enables automatic line-ending processing.  It has two separate
	    effects.  First, it automatically chomps $/ (the input record
	    separator) when used with -n or -p.	 Second, it assigns "$\" (the
	    output record separator) to have the value of octnum so that any
	    print statements will have that separator added back on.  If
	    octnum is omitted, sets "$\" to the current value of $/.  For
	    instance, to trim lines to 80 columns:

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

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

		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

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

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

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

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

       -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

	    Also note that "<>" passes command line arguments to "open" in
	    perlfunc, which doesn't necessarily interpret them as file names.
	    See	 perlop for possible security implications.

	    Here is an efficient way to delete all files that haven't been
	    modified for at least a week:

		find . -mtime +7 -print | perl -nle unlink

	    This is faster than using the -exec switch of find because you
	    don't have to start a process on every filename found.  It does
	    suffer from the bug of mishandling newlines in pathnames, which
	    you can fix if you follow the example under -0.

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

       -p   causes Perl to assume the following loop around your program,
	    which makes it iterate over filename arguments somewhat like sed:

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

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

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

       -s   enables rudimentary switch parsing for switches on the command
	    line after the program name but before any filename arguments (or
	    before an argument of --).	Any switch found there is removed from
	    @ARGV and sets the corresponding variable in the Perl program.
	    The following program prints "1" if the program is invoked with a
	    -xyz switch, and "abc" if it is invoked with -xyz=abc.

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

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

       -S   makes Perl use the PATH environment variable to search for the
	    program unless the name of the program contains path separators.

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

	    Typically this is used to emulate "#!" startup on platforms that
	    don't support "#!".	 It's also convenient when debugging a script
	    that uses "#!", and is thus normally found by the shell's $PATH
	    search mechanism.

	    This example works on many platforms that have a shell compatible
	    with Bourne shell:

		eval 'exec /usr/bin/perl -wS $0 ${1+"$@"}'
			if $running_under_some_shell;

	    The system ignores the first line and feeds the program to
	    /bin/sh, which proceeds to try to execute the Perl program as a
	    shell script.  The shell executes the second line as a normal
	    shell command, and thus starts up the Perl interpreter.  On some
	    systems $0 doesn't always contain the full pathname, so the -S
	    tells Perl to search for the program if necessary.	After Perl
	    locates the program, it parses the lines and ignores them because
	    the variable $running_under_some_shell is never true.  If the
	    program will be interpreted by csh, you will need to replace
	    "${1+"$@"}" with $*, even though that doesn't understand embedded
	    spaces (and such) in the argument list.  To start up sh rather
	    than csh, some systems may have to replace the "#!" line with a
	    line containing just a colon, which will be politely ignored by
	    Perl.  Other systems can't control that, and need a totally
	    devious construct that will work under any of csh, sh, or Perl,
	    such as the following:

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

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

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

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

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

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

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

       -U   allows Perl to do unsafe operations.  Currently the only "unsafe"
	    operations are attempting to unlink directories while running as
	    superuser and running setuid programs with fatal taint checks
	    turned into warnings.  Note that warnings must be enabled along
	    with this option to actually generate the taint-check warnings.

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

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

	    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 ";",
	    allowing you to embed queries into shell commands.	(mnemonic:
	    PATH separator ":".)

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

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

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

	    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

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

       -w   prints warnings about dubious constructs, such as variable names
	    mentioned only once and scalar variables used before being set;
	    redefined subroutines; references to undefined filehandles;
	    filehandles opened read-only that you are attempting to write on;
	    values used as a number that don't look like numbers; using an
	    array as though it were a scalar; if your subroutines recurse more
	    than 100 deep; and innumerable other things.

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

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

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

	    tells Perl that the program is embedded in a larger chunk of
	    unrelated text, such as in a mail message.	Leading garbage will
	    be discarded until the first line that starts with "#!" and
	    contains the string "perl".	 Any meaningful switches on that line
	    will be applied.

	    All references to line numbers by the program (warnings, errors,
	    ...)  will treat the "#!" line as the first line.  Thus a warning
	    on the 2nd line of the program, which is on the 100th line in the
	    file will be reported as line 2, not as line 100.  This can be
	    overridden by using the "#line" directive.	(See "Plain Old
	    Comments (Not!)" in perlsyn)

	    If a directory name is specified, Perl will switch to that
	    directory before running the program.  The -x switch controls only
	    the disposal of leading garbage.  The program must be terminated
	    with "__END__" if there is trailing garbage to be ignored;	the
	    program can process any or all of the trailing garbage via the
	    "DATA" filehandle if desired.

	    The directory, if specified, must appear immediately following the
	    -x with no intervening whitespace.

       HOME	   Used if "chdir" has no argument.

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

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

       PERL5LIB	   A list of directories in which to look for Perl library
		   files before looking in the standard library and the
		   current directory.  Any architecture-specific and version-
		   specific directories, such as version/archname/, version/,
		   or archname/ under the specified locations are
		   automatically included if they exist, with this lookup done
		   at interpreter startup time.	 In addition, any directories
		   matching the entries in $Config{inc_version_list} are
		   added.  (These typically would be for older compatible perl
		   versions installed in the same directory tree.)

		   If PERL5LIB is not defined, PERLLIB is used.	 Directories
		   are separated (like in PATH) by a colon on Unixish
		   platforms and by a semicolon on Windows (the proper path
		   separator being given by the command "perl -V:path_sep").

		   When running taint checks, either because the program was
		   running setuid or setgid, or the -T or -t switch was
		   specified, neither PERL5LIB nor PERLLIB is consulted. The
		   program should instead say:

		       use lib "/my/directory";

       PERL5OPT	   Command-line options (switches).  Switches in this variable
		   are treated as if they were on every Perl command line.
		   Only the -[CDIMUdmtwW] switches are allowed.	 When running
		   taint checks (either because the program was running setuid
		   or setgid, or because the -T or -t switch was used), this
		   variable is ignored.	 If PERL5OPT begins with -T, tainting
		   will be enabled and subsequent options ignored.  If
		   PERL5OPT begins with -t, tainting will be enabled, a
		   writable dot removed from @INC, and subsequent options

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

		   It is conventional to start layer names with a colon (for
		   example, ":perlio") to emphasize their similarity to
		   variable "attributes". But the code that parses layer
		   specification strings, which is also used to decode the
		   PERLIO environment variable, treats the colon as a

		   An unset or empty PERLIO is equivalent to the default set
		   of layers for your platform; for example, ":unix:perlio" on
		   Unix-like systems and ":unix:crlf" on Windows and other
		   DOS-like systems.

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

		   Layers it makes sense to include in the PERLIO environment
		   variable are briefly summarized below. For more details see

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

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

		   :mmap   A layer that implements "reading" of files by using
			   mmap(2) to make an entire file appear in the
			   process's address space, and then using that as
			   PerlIO's "buffer".

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

		   :pop	   An experimental pseudolayer that removes the
			   topmost layer.  Use with the same care as is
			   reserved for nitroglycerine.

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

			   Unlike in earlier versions of Perl, ":raw" is not
			   just the inverse of ":crlf": other layers which
			   would affect the binary nature of the stream are
			   also removed or disabled.

		   :stdio  This layer provides a PerlIO interface by wrapping
			   system's ANSI C "stdio" library calls. The layer
			   provides both buffering and IO.  Note that the
			   ":stdio" layer does not do CRLF translation even if
			   that is the platform's normal behaviour. You will
			   need a ":crlf" layer above it to do that.

		   :unix   Low-level layer that calls "read", "write",
			   "lseek", etc.

		   :utf8   A pseudolayer that enables a flag in the layer
			   below to tell Perl that output should be in utf8
			   and that input should be regarded as already in
			   valid utf8 form. WARNING: It does not check for
			   validity and as such should be handled with extreme
			   caution for input, because security violations can
			   occur with non-shortest UTF-8 encodings, etc.
			   Generally ":encoding(utf8)" is the best option when
			   reading UTF-8 encoded data.

		   :win32  On Win32 platforms this experimental layer uses
			   native "handle" IO rather than a Unix-like numeric
			   file descriptor layer. Known to be buggy in this
			   release (5.14).

		   The default set of layers should give acceptable results on
		   all platforms

		   For Unix platforms that will be the equivalent of "unix
		   perlio" or "stdio".	Configure is set up to prefer the
		   "stdio" implementation if the system's library provides for
		   fast access to the buffer; otherwise, it uses the "unix
		   perlio" implementation.

		   On Win32 the default in this release (5.14) is "unix crlf".
		   Win32's "stdio" has a number of bugs/mis-features for Perl
		   IO which are somewhat depending on the version and vendor
		   of the C compiler. Using our own "crlf" layer as the buffer
		   avoids those issues and makes things more uniform.  The
		   "crlf" layer provides CRLF conversion as well as buffering.

		   This release (5.14) uses "unix" as the bottom layer on
		   Win32, and so still uses the C compiler's numeric file
		   descriptor routines. There is an experimental native
		   "win32" layer, which is expected to be enhanced and should
		   eventually become the default under Win32.

		   The PERLIO environment variable is completely ignored when
		   Perl is run in taint mode.

		   If set to the name of a file or device, certain operations
		   of PerlIO subsystem will be logged to that file, which is
		   opened in append mode.  Typical uses are in Unix:

		      % env PERLIO_DEBUG=/dev/tty perl script ...

		   and under Win32, the approximately equivalent:

		      > set PERLIO_DEBUG=CON
		      perl script ...

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

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

		   The PERLLIB environment variable is completely ignored when
		   Perl is run in taint mode.

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

			   BEGIN { require "" }

		   The PERL5DB environment variable is only used when Perl is
		   started with a bare -d switch.

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

       PERL5SHELL (specific to the Win32 port)
		   On Win32 ports only, may be set to an alternative shell
		   that Perl must use internally for executing "backtick"
		   commands or system().  Default is "cmd.exe /x/d/c" on
		   WindowsNT and " /c" on Windows95.	 The value is
		   considered space-separated.	Precede any character that
		   needs to be protected, like a space or backslash, with
		   another backslash.

		   Note that Perl doesn't use COMSPEC for this purpose because
		   COMSPEC has a high degree of variability among users,
		   leading to portability concerns.  Besides, Perl can use a
		   shell that may not be fit for interactive use, and setting
		   COMSPEC to such a shell may interfere with the proper
		   functioning of other programs (which usually look in
		   COMSPEC to find a shell fit for interactive use).

		   Before Perl 5.10.0 and 5.8.8, PERL5SHELL was not taint
		   checked when running external commands.  It is recommended
		   that you explicitly set (or delete) $ENV{PERL5SHELL} when
		   running in taint mode under Windows.

       PERL_ALLOW_NON_IFS_LSP (specific to the Win32 port)
		   Set to 1 to allow the use of non-IFS compatible LSPs
		   (Layered Service Providers).	 Perl normally searches for an
		   IFS-compatible LSP because this is required for its
		   emulation of Windows sockets as real filehandles.  However,
		   this may cause problems if you have a firewall such as
		   McAfee Guardian, which requires that all applications use
		   its LSP but which is not IFS-compatible, because clearly
		   Perl will normally avoid using such an LSP.

		   Setting this environment variable to 1 means that Perl will
		   simply use the first suitable LSP enumerated in the
		   catalog, which keeps McAfee Guardian happy--and in that
		   particular case Perl still works too because McAfee
		   Guardian's LSP actually plays other games which allow
		   applications requiring IFS compatibility to work.

		   Relevant only if Perl is compiled with the "malloc"
		   included with the Perl distribution; that is, if "perl
		   -V:d_mymalloc" is "define".

		   If set, this dumps out memory statistics after execution.
		   If set to an integer greater than one, also dumps out
		   memory statistics after compilation.

		   Relevant only if your Perl executable was built with
		   -DDEBUGGING, this controls the behaviour of global
		   destruction of objects and other references.	 See
		   "PERL_DESTRUCT_LEVEL" in perlhacktips for more information.

		   Set to "1" to have Perl resolve all undefined symbols when
		   it loads a dynamic library.	The default behaviour is to
		   resolve symbols when they are used.	Setting this variable
		   is useful during testing of extensions, as it ensures that
		   you get an error on misspelled function names even if the
		   test suite doesn't call them.

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

		   (Since Perl 5.8.1, new semantics in Perl 5.18.0)  Used to
		   override the randomization of Perl's internal hash
		   function. The value is expressed in hexadecimal, and may
		   include a leading 0x. Truncated patterns are treated as
		   though they are suffixed with sufficient 0's as required.

		   If the option is provided, and "PERL_PERTURB_KEYS" is NOT
		   set, then a value of '0' implies "PERL_PERTURB_KEYS=0" and
		   any other value implies "PERL_PERTURB_KEYS=2".

		   PLEASE NOTE: The hash seed is sensitive information. Hashes
		   are randomized to protect against local and remote attacks
		   against Perl code. By manually setting a seed, this
		   protection may be partially or completely lost.

		   See "Algorithmic Complexity Attacks" in perlsec and

		   (Since Perl 5.18.0)	Set to "0" or "NO" then traversing
		   keys will be repeatable from run to run for the same
		   PERL_HASH_SEED.  Insertion into a hash will not change the
		   order, except to provide for more space in the hash. When
		   combined with setting PERL_HASH_SEED this mode is as close
		   to pre 5.18 behavior as you can get.

		   When set to "1" or "RANDOM" then traversing keys will be
		   randomized.	Every time a hash is inserted into the key
		   order will change in a random fashion. The order may not be
		   repeatable in a following program run even if the
		   PERL_HASH_SEED has been specified. This is the default mode
		   for perl.

		   When set to "2" or "DETERMINISTIC" then inserting keys into
		   a hash will cause the key order to change, but in a way
		   that is repeatable from program run to program run.

		   NOTE: Use of this option is considered insecure, and is
		   intended only for debugging non-deterministic behavior in
		   Perl's hash function. Do not use it in production.

		   See "Algorithmic Complexity Attacks" in perlsec and
		   information. You can get and set the key traversal mask for
		   a specific hash by using the "hash_traversal_mask()"
		   function from Hash::Util.

		   (Since Perl 5.8.1.)	Set to "1" to display (to STDERR)
		   information about the hash function, seed, and what type of
		   key traversal randomization is in effect at the beginning
		   of execution.  This, combined with "PERL_HASH_SEED" and
		   "PERL_PERTURB_KEYS" is intended to aid in debugging
		   nondeterministic behaviour caused by hash randomization.

		   Note that any information about the hash function,
		   especially the hash seed is sensitive information: by
		   knowing it, one can craft a denial-of-service attack
		   against Perl code, even remotely; see "Algorithmic
		   Complexity Attacks" in perlsec for more information. Do not
		   disclose the hash seed to people who don't need to know it.
		   See also "hash_seed()" and "key_traversal_mask()" in

		   An example output might be:


		   If your Perl was configured with -Accflags=-DPERL_MEM_LOG,
		   setting the environment variable "PERL_MEM_LOG" enables
		   logging debug messages. The value has the form
		   "<number>[m][s][t]", where "number" is the file descriptor
		   number you want to write to (2 is default), and the
		   combination of letters specifies that you want information
		   about (m)emory and/or (s)v, optionally with (t)imestamps.
		   For example, "PERL_MEM_LOG=1mst" logs all information to
		   stdout. You can write to other opened file descriptors in a
		   variety of ways:

		     $ 3>foo3 PERL_MEM_LOG=3m perl ...

       PERL_ROOT (specific to the VMS port)
		   A translation-concealed rooted logical name that contains
		   Perl and the logical device for the @INC path on VMS only.
		   Other logical names that affect Perl on VMS include
		   but are optional and discussed further in perlvms and in
		   README.vms in the Perl source distribution.

		   Available in Perls 5.8.1 and later.	If set to "unsafe",
		   the pre-Perl-5.8.0 signal behaviour (which is immediate but
		   unsafe) is restored.	 If set to "safe", then safe (but
		   deferred) signals are used.	See "Deferred Signals (Safe
		   Signals)" in perlipc.

		   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

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

       Perl and its various modules and components, including its test
       frameworks, may sometimes make use of certain other environment
       variables.  Some of these are specific to a particular platform.
       Please consult the appropriate module documentation and any
       documentation for your platform (like perlsolaris, perllinux,
       perlmacosx, perlwin32, etc) for variables peculiar to those specific

       Perl makes all environment variables available to the program being
       executed, and passes these along to any child processes it starts.
       However, programs running setuid would do well to execute the following
       lines before doing anything else, just to keep people honest:

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

perl v5.18.2			  2014-01-06			PERLRUN(1perl)

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