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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|-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 behavior regardless of how Perl was
       invoked, even if -x was used to find the beginning of the program.

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

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

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

	   #! -*-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, perl5.005_57, you should place that directly in
       the #! line's path.

       If the #! line does not contain the word "perl", the program named
       after the #! is executed instead of the Perl interpreter.  This is
       slightly bizarre, but it helps people on machines that don't do #!,
       because they can tell a program that their SHELL is /usr/bin/perl, and
       Perl will then dispatch the program to the correct interpreter for

       After locating your program, Perl compiles the entire program to an
       internal form.  If there are any compilation errors, execution of the
       program is not attempted.  (This is unlike the typical shell script,
       which might run 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

	   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: .

       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\""

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

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

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

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

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

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

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

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

       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 5.005_54;

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

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

       Switches include:

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

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

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

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

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

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

	    is equivalent to

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

	    An alternate delimiter may be specified using -F.

       -C [number/list]
	    The "-C" flag controls some 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) will have the ":utf8" PerlIO layer implicitly applied
	    to them, in other words, UTF-8 is expected from any input stream,
	    and UTF-8 is produced to any output stream.	 This is just the
	    default, with explicit layers in open() and with binmode() one can
	    manipulate streams as usual.

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

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

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

	    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 "BEGIN",
	    "UNITCHECK", "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 (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, preprocessor command for -P, 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  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
	      2097152  C  Copy On Write
	      4194304  A  Consistency checks on internal structures
	      8388608  q  quiet - currently only suppresses the "EXECUTING" message

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

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

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

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

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

	    See perldebug for details and variations.

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

       -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.

	    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, no backup is made and the current
	    file is overwritten.

	    If the extension doesn't contain a "*", then it is appended to the
	    end of the current filename as a suffix.  If the extension does
	    contain one or more "*" characters, then each "*" is replaced with
	    the current filename.  In Perl terms, you could think of this as:

		($backup = $extension) =~ s/\*/$file_name/g;

	    This allows you to add a prefix to the backup file, instead of (or
	    in addition to) a suffix:

		$ perl -pi'orig_*' -e 's/bar/baz/' fileA    # backup to 'orig_fileA'

	    Or even to place backup copies of the original files into another
	    directory (provided the directory already exists):

		$ perl -pi'old/*.orig' -e 's/bar/baz/' fileA # backup to 'old/fileA.orig'

	    These sets of one-liners are equivalent:

		$ perl -pi -e 's/bar/baz/' fileA	    # overwrite current file
		$ perl -pi'*' -e 's/bar/baz/' fileA	    # overwrite current file

		$ perl -pi'.orig' -e 's/bar/baz/' fileA	    # backup to 'fileA.orig'
		$ perl -pi'*.orig' -e 's/bar/baz/' fileA    # backup to 'fileA.orig'

	    From the shell, saying

		$ perl -p -i.orig -e "s/foo/bar/; ... "

	    is the same as using the program:

		#!/usr/bin/perl -pi.orig

	    which is equivalent to

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

	    except that the -i form doesn't need to compare $ARGV to $oldargv
	    to know when the filename has changed.  It does, however, use
	    ARGVOUT for the selected filehandle.  Note that STDOUT is restored
	    as the default output filehandle after the loop.

	    As shown above, Perl creates the backup file whether or not any
	    output is actually changed.	 So this is just a fancy way to copy

		$ 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), and also tells the C preprocessor where to search
	    for include files.	The C preprocessor is invoked with -P; by
	    default it searches /usr/include and /usr/lib/perl.

	    enables automatic line-ending processing.  It has two separate
	    effects.  First, it automatically chomps $/ (the input record
	    separator) when used with -n or -p.	 Second, it assigns "$\" (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 -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

	    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.

       -P   NOTE: Use of -P is strongly discouraged because of its inherent
	    problems, including poor portability. It is deprecated and will be
	    removed in a future version of Perl.

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

	    If you're considering using "-P", you might also want to look at
	    the Filter::cpp module from CPAN.

	    The problems of -P include, but are not limited to:

	    ·	      The "#!" line is stripped, so any switches there don't

	    ·	      A "-P" on a "#!" line doesn't work.

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

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


		      because after -P this will became illegal 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
	    spurious "used only once" warnings.

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

	    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 #!.  Its also convenient when debugging a script
	    that uses #!, and is thus normally found by the shell's $PATH
	    search mechanism.

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

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

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

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

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

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

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

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

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

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

       -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
	    variable) must be used along with this option to actually generate
	    the taint-check warnings.

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

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

	    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
	    that are mentioned only once and scalar variables that are used
	    before being set, redefined subroutines, references to undefined
	    filehandles or filehandles opened read-only that you are
	    attempting to write on, values used as a number that don't look
	    like numbers, using an array as though it were a scalar, if your
	    subroutines recurse more than 100 deep, and innumerable other

	    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

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

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

	    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, and 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 directories
		   under the specified locations are automatically included if
		   they exist (this lookup being done at interpreter startup

		   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 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 -[CDIMUdmtw] switches are allowed.  When running taint
		   checks (because the program was running setuid or setgid,
		   or the -T switch was used), this variable is ignored.  If
		   PERL5OPT begins with -T, tainting will be enabled, and any
		   subsequent options ignored.

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

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

		   An unset or empty PERLIO is equivalent to the 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.

		   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

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

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

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

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

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

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

		   :unix   Low level layer which calls "read", "write" and
			   "lseek" etc.

		   :utf8   A pseudolayer that turns on a flag on the layer
			   below to tell perl that output should be in utf8
			   and that input should be regarded as already in
			   valid utf8 form. It does not check for validity and
			   as such should be handled with caution for input.
			   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 unix-like numeric
			   file descriptor layer. Known to be buggy in this

		   On all platforms the default set of layers should give
		   acceptable results.

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

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

		   This release uses "unix" as the bottom layer on Win32 and
		   so still uses C compiler's numeric file descriptor
		   routines. There is an experimental native "win32" layer
		   which is expected to be enhanced and should eventually be
		   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 then certain
		   operations of PerlIO sub-system will be logged to that file
		   (opened as append). Typical uses are UNIX:

		      PERLIO_DEBUG=/dev/tty perl script ...

		   and Win32 approximate equivalent:

		      set PERLIO_DEBUG=CON
		      perl script ...

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

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

		   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 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)
		   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 to be space-
		   separated.  Precede any character that needs to be
		   protected (like a space or backslash) with a backslash.

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

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

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

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

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

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

		   (Since Perl 5.8.1.)	Used to randomise perl's internal hash
		   function.  To emulate the pre-5.8.1 behaviour, set to an
		   integer (zero means exactly the same order as 5.8.0).
		   "Pre-5.8.1" means, among other things, that hash keys will
		   always have the same ordering between different runs of

		   Most hashes return elements in the same order as Perl 5.8.0
		   by default.	On a hash by hash basis, if pathological data
		   is detected during a hash key insertion, then that hash
		   will switch to an alternative random hash seed.

		   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.

		   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

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

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

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

		   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.

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

	   $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 v5.10.1			  2009-07-26			    PERLRUN(1)

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