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RedHat 9 (Linux i386) - man page for pod::usage (redhat section 3pm)

Pod::Usage(3pm) 		 Perl Programmers Reference Guide		  Pod::Usage(3pm)

       Pod::Usage, pod2usage() - print a usage message from embedded pod documentation

	 use Pod::Usage

	 my $message_text  = "This text precedes the usage message.";
	 my $exit_status   = 2; 	 ## The exit status to use
	 my $verbose_level = 0; 	 ## The verbose level to use
	 my $filehandle    = \*STDERR;	 ## The filehandle to write to



	 pod2usage( { -message => $message_text ,
		      -exitval => $exit_status	,
		      -verbose => $verbose_level,
		      -output  => $filehandle } );

	 pod2usage(   -msg     => $message_text ,
		      -exitval => $exit_status	,
		      -verbose => $verbose_level,
		      -output  => $filehandle	);

       pod2usage should be given either a single argument, or a list of arguments corresponding
       to an associative array (a "hash"). When a single argument is given, it should correspond
       to exactly one of the following:

       o   A string containing the text of a message to print before printing the usage message

       o   A numeric value corresponding to the desired exit status

       o   A reference to a hash

       If more than one argument is given then the entire argument list is assumed to be a hash.
       If a hash is supplied (either as a reference or as a list) it should contain one or more
       elements with the following keys:

	   The text of a message to print immediately prior to printing the program's usage mes-

	   The desired exit status to pass to the exit() function.  This should be an integer, or
	   else the string "NOEXIT" to indicate that control should simply be returned without
	   terminating the invoking process.

	   The desired level of "verboseness" to use when printing the usage message. If the cor-
	   responding value is 0, then only the "SYNOPSIS" section of the pod documentation is
	   printed. If the corresponding value is 1, then the "SYNOPSIS" section, along with any
	   section entitled "OPTIONS", "ARGUMENTS", or "OPTIONS AND ARGUMENTS" is printed.  If
	   the corresponding value is 2 or more then the entire manpage is printed.

	   A reference to a filehandle, or the pathname of a file to which the usage message
	   should be written. The default is "\*STDERR" unless the exit value is less than 2 (in
	   which case the default is "\*STDOUT").

	   A reference to a filehandle, or the pathname of a file from which the invoking
	   script's pod documentation should be read.  It defaults to the file indicated by $0
	   ($PROGRAM_NAME for users of English.pm).

	   A list of directory paths. If the input file does not exist, then it will be searched
	   for in the given directory list (in the order the directories appear in the list). It
	   defaults to the list of directories implied by $ENV{PATH}. The list may be specified
	   either by a reference to an array, or by a string of directory paths which use the
	   same path separator as $ENV{PATH} on your system (e.g., ":" for Unix, ";" for MSWin32
	   and DOS).

       pod2usage will print a usage message for the invoking script (using its embedded pod docu-
       mentation) and then exit the script with the desired exit status. The usage message
       printed may have any one of three levels of "verboseness": If the verbose level is 0, then
       only a synopsis is printed. If the verbose level is 1, then the synopsis is printed along
       with a description (if present) of the command line options and arguments. If the verbose
       level is 2, then the entire manual page is printed.

       Unless they are explicitly specified, the default values for the exit status, verbose
       level, and output stream to use are determined as follows:

       o   If neither the exit status nor the verbose level is specified, then the default is to
	   use an exit status of 2 with a verbose level of 0.

       o   If an exit status is specified but the verbose level is not, then the verbose level
	   will default to 1 if the exit status is less than 2 and will default to 0 otherwise.

       o   If an exit status is not specified but verbose level is given, then the exit status
	   will default to 2 if the verbose level is 0 and will default to 1 otherwise.

       o   If the exit status used is less than 2, then output is printed on "STDOUT".	Otherwise
	   output is printed on "STDERR".

       Although the above may seem a bit confusing at first, it generally does "the right thing"
       in most situations.  This determination of the default values to use is based upon the
       following typical Unix conventions:

       o   An exit status of 0 implies "success". For example, diff(1) exits with a status of 0
	   if the two files have the same contents.

       o   An exit status of 1 implies possibly abnormal, but non-defective, program termination.
	   For example, grep(1) exits with a status of 1 if it did not find a matching line for
	   the given regular expression.

       o   An exit status of 2 or more implies a fatal error. For example, ls(1) exits with a
	   status of 2 if you specify an illegal (unknown) option on the command line.

       o   Usage messages issued as a result of bad command-line syntax should go to "STDERR".
	   However, usage messages issued due to an explicit request to print usage (like speci-
	   fying -help on the command line) should go to "STDOUT", just in case the user wants to
	   pipe the output to a pager (such as more(1)).

       o   If program usage has been explicitly requested by the user, it is often desireable to
	   exit with a status of 1 (as opposed to 0) after issuing the user-requested usage mes-
	   sage.  It is also desireable to give a more verbose description of program usage in
	   this case.

       pod2usage doesn't force the above conventions upon you, but it will use them by default if
       you don't expressly tell it to do otherwise.  The ability of pod2usage() to accept a sin-
       gle number or a string makes it convenient to use as an innocent looking error message
       handling function:

	   use Pod::Usage;
	   use Getopt::Long;

	   ## Parse options
	   GetOptions("help", "man", "flag1")  ||  pod2usage(2);
	   pod2usage(1)  if ($opt_help);
	   pod2usage(-verbose => 2)  if ($opt_man);

	   ## Check for too many filenames
	   pod2usage("$0: Too many files given.\n")  if (@ARGV > 1);

       Some user's however may feel that the above "economy of expression" is not particularly
       readable nor consistent and may instead choose to do something more like the following:

	   use Pod::Usage;
	   use Getopt::Long;

	   ## Parse options
	   GetOptions("help", "man", "flag1")  ||  pod2usage(-verbose => 0);
	   pod2usage(-verbose => 1)  if ($opt_help);
	   pod2usage(-verbose => 2)  if ($opt_man);

	   ## Check for too many filenames
	   pod2usage(-verbose => 2, -message => "$0: Too many files given.\n")
	       if (@ARGV > 1);

       As with all things in Perl, there's more than one way to do it, and pod2usage() adheres to
       this philosophy.  If you are interested in seeing a number of different ways to invoke
       pod2usage (although by no means exhaustive), please refer to "EXAMPLES".

       Each of the following invocations of "pod2usage()" will print just the "SYNOPSIS" section
       to "STDERR" and will exit with a status of 2:



	   pod2usage(-verbose => 0);

	   pod2usage(-exitval => 2);

	   pod2usage({-exitval => 2, -output => \*STDERR});

	   pod2usage({-verbose => 0, -output  => \*STDERR});

	   pod2usage(-exitval => 2, -verbose => 0);

	   pod2usage(-exitval => 2, -verbose => 0, -output => \*STDERR);

       Each of the following invocations of "pod2usage()" will print a message of "Syntax error."
       (followed by a newline) to "STDERR", immediately followed by just the "SYNOPSIS" section
       (also printed to "STDERR") and will exit with a status of 2:

	   pod2usage("Syntax error.");

	   pod2usage(-message => "Syntax error.", -verbose => 0);

	   pod2usage(-msg  => "Syntax error.", -exitval => 2);

	   pod2usage({-msg => "Syntax error.", -exitval => 2, -output => \*STDERR});

	   pod2usage({-msg => "Syntax error.", -verbose => 0, -output => \*STDERR});

	   pod2usage(-msg  => "Syntax error.", -exitval => 2, -verbose => 0);

	   pod2usage(-message => "Syntax error.",
		     -exitval => 2,
		     -verbose => 0,
		     -output  => \*STDERR);

       Each of the following invocations of "pod2usage()" will print the "SYNOPSIS" section and
       any "OPTIONS" and/or "ARGUMENTS" sections to "STDOUT" and will exit with a status of 1:


	   pod2usage(-verbose => 1);

	   pod2usage(-exitval => 1);

	   pod2usage({-exitval => 1, -output => \*STDOUT});

	   pod2usage({-verbose => 1, -output => \*STDOUT});

	   pod2usage(-exitval => 1, -verbose => 1);

	   pod2usage(-exitval => 1, -verbose => 1, -output => \*STDOUT});

       Each of the following invocations of "pod2usage()" will print the entire manual page to
       "STDOUT" and will exit with a status of 1:

	   pod2usage(-verbose  => 2);

	   pod2usage({-verbose => 2, -output => \*STDOUT});

	   pod2usage(-exitval  => 1, -verbose => 2);

	   pod2usage({-exitval => 1, -verbose => 2, -output => \*STDOUT});

       Recommended Use

       Most scripts should print some type of usage message to "STDERR" when a command line syn-
       tax error is detected. They should also provide an option (usually "-H" or "-help") to
       print a (possibly more verbose) usage message to "STDOUT". Some scripts may even wish to
       go so far as to provide a means of printing their complete documentation to "STDOUT" (per-
       haps by allowing a "-man" option). The following complete example uses Pod::Usage in com-
       bination with Getopt::Long to do all of these things:

	   use Getopt::Long;
	   use Pod::Usage;

	   my $man = 0;
	   my $help = 0;
	   ## Parse options and print usage if there is a syntax error,
	   ## or if usage was explicitly requested.
	   GetOptions('help|?' => \$help, man => \$man) or pod2usage(2);
	   pod2usage(1) if $help;
	   pod2usage(-verbose => 2) if $man;

	   ## If no arguments were given, then allow STDIN to be used only
	   ## if it's not connected to a terminal (otherwise print usage)
	   pod2usage("$0: No files given.")  if ((@ARGV == 0) && (-t STDIN));

	   =head1 NAME

	   sample - Using GetOpt::Long and Pod::Usage

	   =head1 SYNOPSIS

	   sample [options] [file ...]

	      -help	       brief help message
	      -man	       full documentation

	   =head1 OPTIONS

	   =over 8

	   =item B<-help>

	   Print a brief help message and exits.

	   =item B<-man>

	   Prints the manual page and exits.


	   =head1 DESCRIPTION

	   B<This program> will read the given input file(s) and do something
	   useful with the contents thereof.


       By default, pod2usage() will use $0 as the path to the pod input file.  Unfortunately, not
       all systems on which Perl runs will set $0 properly (although if $0 isn't found,
       pod2usage() will search $ENV{PATH} or else the list specified by the "-pathlist" option).
       If this is the case for your system, you may need to explicitly specify the path to the
       pod docs for the invoking script using something similar to the following:

	   pod2usage(-exitval => 2, -input => "/path/to/your/pod/docs");

       Brad Appleton <bradapp@enteract.com>

       Based on code for Pod::Text::pod2text() written by Tom Christiansen <tchrist@mox.perl.com>

       Steven McDougall <swmcd@world.std.com> for his help and patience with re-writing this man-

perl v5.8.0				    2002-06-01				  Pod::Usage(3pm)

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