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MAN page from Fedora 18 perl-Pod-Parser-1.51-235.fc18.noarch.rpm

Pod::Usage

Section: Perl Programmers Reference Guide (3pm)
Updated: 2012-10-11
Index 

NAME

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

SYNOPSIS

  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_text);  pod2usage($exit_status);  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(   -verbose => 2,               -noperldoc => 1  )
 

ARGUMENTS

pod2usage should be given either a single argument, or a list ofarguments corresponding to an associative array (a ``hash''). When a singleargument is given, it should correspond to exactly one of the following:
*
A string containing the text of a message to print before printingthe usage message
*
A numeric value corresponding to the desired exit status
*
A reference to a hash

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

-message
-msg
The text of a message to print immediately prior to printing theprogram's usage message.
-exitval
The desired exit status to pass to the exit() function.This should be an integer, or else the string ``NOEXIT'' toindicate that control should simply be returned withoutterminating the invoking process.
-verbose
The desired level of ``verboseness'' to use when printing the usagemessage. If the corresponding value is 0, then only the ``SYNOPSIS''section of the pod documentation is printed. If the corresponding valueis 1, then the ``SYNOPSIS'' section, along with any section entitled``OPTIONS'', ``ARGUMENTS'', or ``OPTIONS AND ARGUMENTS'' is printed. If thecorresponding value is 2 or more then the entire manpage is printed.

The special verbosity level 99 requires to also specify the -sectionsparameter; then these sections are extracted (see Pod::Select)and printed.

-sections
A string representing a selection list for sections to be printedwhen -verbose is set to 99, e.g. "NAME|SYNOPSIS|DESCRIPTION|VERSION".

Alternatively, an array reference of section specifications can be used:

  pod2usage(-verbose => 99,             -sections => [ qw(fred fred/subsection) ] );
-output
A reference to a filehandle, or the pathname of a file to which theusage message should be written. The default is "\*STDERR" unless theexit value is less than 2 (in which case the default is "\*STDOUT").
-input
A reference to a filehandle, or the pathname of a file from which theinvoking script's pod documentation should be read. It defaults to thefile indicated by $0 ($PROGRAM_NAME for users of English.pm).

If you are calling pod2usage() from a module and want to displaythat module's POD, you can use this:

  use Pod::Find qw(pod_where);  pod2usage( -input => pod_where({-inc => 1}, __PACKAGE__) );
-pathlist
A list of directory paths. If the input file does not exist, then itwill be searched for in the given directory list (in the order thedirectories appear in the list). It defaults to the list of directoriesimplied by $ENV{PATH}. The list may be specified either by a referenceto an array, or by a string of directory paths which use the same pathseparator as $ENV{PATH} on your system (e.g., ":" for Unix, ";" forMSWin32 and DOS).
-noperldoc
By default, Pod::Usage will call perldoc when -verbose >= 2 isspecified. This does not work well e.g. if the script was packedwith PAR. The -noperldoc option suppresses the external call toperldoc and uses the simple text formatter (Pod::Text) to output the POD.
 

Pass-through options

The following options are passed through to the underlying text formatter(Pod::Text or Pod::PlainText for Perl versions < 5.005_58). See the manual pages of these modules for more information.

  alt code indent loose margin quotes sentence stderr utf8 width
 

DESCRIPTION

pod2usage will print a usage message for the invoking script (usingits embedded pod documentation) and then exit the script with thedesired exit status. The usage message printed may have any one of threelevels of ``verboseness'': If the verbose level is 0, then only a synopsisis printed. If the verbose level is 1, then the synopsis is printedalong with a description (if present) of the command line options andarguments. If the verbose level is 2, then the entire manual page isprinted.

Unless they are explicitly specified, the default values for the exitstatus, verbose level, and output stream to use are determined asfollows:

*
If neither the exit status nor the verbose level is specified, then thedefault is to use an exit status of 2 with a verbose level of 0.
*
If an exit status is specified but the verbose level is not, then theverbose level will default to 1 if the exit status is less than 2 andwill default to 0 otherwise.
*
If an exit status is not specified but verbose level is given, thenthe exit status will default to 2 if the verbose level is 0 and willdefault to 1 otherwise.
*
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 defaultvalues to use is based upon the following typical Unix conventions:

*
An exit status of 0 implies ``success''. For example, diff(1) exitswith a status of 0 if the two files have the same contents.
*
An exit status of 1 implies possibly abnormal, but non-defective, programtermination. For example, grep(1) exits with a status of 1 ifit did not find a matching line for the given regular expression.
*
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 onthe command line.
*
Usage messages issued as a result of bad command-line syntax should goto "STDERR". However, usage messages issued due to an explicit requestto print usage (like specifying -help on the command line) should goto "STDOUT", just in case the user wants to pipe the output to a pager(such as more(1)).
*
If program usage has been explicitly requested by the user, it is oftendesirable to exit with a status of 1 (as opposed to 0) after issuingthe user-requested usage message. It is also desirable to give amore verbose description of program usage in this case.

pod2usage doesn't force the above conventions upon you, but it willuse them by default if you don't expressly tell it to do otherwise. Theability of pod2usage() to accept a single number or a string makes itconvenient 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'' isnot particularly readable nor consistent and may instead choose to dosomething 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, andpod2usage() adheres to this philosophy. If you are interested inseeing a number of different ways to invoke pod2usage (although by nomeans exhaustive), please refer to ``EXAMPLES''. 

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();    pod2usage(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 messageof ``Syntax error.'' (followed by a newline) to "STDERR", immediatelyfollowed by just the ``SYNOPSIS'' section (also printed to "STDERR") andwill 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(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 theentire 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 acommand line syntax error is detected. They should also provide anoption (usually "-H" or "-help") to print a (possibly more verbose)usage message to "STDOUT". Some scripts may even wish to go so far as toprovide a means of printing their complete documentation to "STDOUT"(perhaps by allowing a "-man" option). The following complete exampleuses Pod::Usage in combination with Getopt::Long to do all of thesethings:

    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));    __END__    =head1 NAME    sample - Using GetOpt::Long and Pod::Usage    =head1 SYNOPSIS    sample [options] [file ...]     Options:       -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.    =back    =head1 DESCRIPTION    B<This program> will read the given input file(s) and do something    useful with the contents thereof.    =cut
 

CAVEATS

By default, pod2usage() will use $0 as the path to the pod inputfile. Unfortunately, not all systems on which Perl runs will set $0properly (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 specifythe path to the pod docs for the invoking script using somethingsimilar to the following:

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

In the pathological case that a script is called via a relative pathand the script itself changes the current working directory(see ``chdir'' in perlfunc) before calling pod2usage, Pod::Usage willfail even on robust platforms. Don't do that. 

AUTHOR

Please report bugs using <http://rt.cpan.org>.

Marek Rouchal <marekrAATTcpan.org>

Brad Appleton <bradappAATTenteract.com>

Based on code for Pod::Text::pod2text() written byTom Christiansen <tchristAATTmox.perl.com> 

ACKNOWLEDGMENTS

Steven McDougall <swmcdAATTworld.std.com> for his help and patiencewith re-writing this manpage. 

SEE ALSO

Pod::Usage is part of the Pod::Parser distribution.

Pod::Parser, Getopt::Long, Pod::Find


 

Index

NAME
SYNOPSIS
ARGUMENTS
Pass-through options
DESCRIPTION
EXAMPLES
Recommended Use
CAVEATS
AUTHOR
ACKNOWLEDGMENTS
SEE ALSO

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