Ubuntu Manpage: Pod::Usage - print a usage message from embedded pod documentation

Provided by: perl-doc_5.26.1-6ubuntu0.7_all

NAME

       Pod::Usage - 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  );

         pod2usage(   -verbose => 2,
                      -perlcmd => $path_to_perl,
                      -perldoc => $path_to_perldoc,
                      -perldocopt => $perldoc_options );

ARGUMENTS

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:

• A string containing the text of a message to print before printing the 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 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:

"-message" string
"-msg" string
The text of a message to print immediately prior to printing the program's usage
message.

"-exitval" value
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.

"-verbose" value
The desired level of "verboseness" to use when printing the usage message. If the
value is 0, then only the "SYNOPSIS" section of the pod documentation is printed. If
the 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, using perldoc if available;
otherwise Pod::Text is used for the formatting. For better readability, the all-
capital headings are downcased, e.g. "SYNOPSIS" => "Synopsis".

The special verbosity level 99 requires to also specify the -sections parameter; then
these sections are extracted and printed.

"-sections" spec
There are two ways to specify the selection. Either a string (scalar) representing a
selection regexp for sections to be printed when -verbose is set to 99, e.g.

"NAME|SYNOPSIS|DESCRIPTION|VERSION"

With the above regexp all content following (and including) any of the given "=head1"
headings will be shown. It is possible to restrict the output to particular
subsections only, e.g.:

"DESCRIPTION/Algorithm"

This will output only the "=head2 Algorithm" heading and content within the "=head1
DESCRIPTION" section. The regexp binding is stronger than the section separator, such
that e.g.:

"DESCRIPTION|OPTIONS|ENVIORNMENT/Caveats"

will print any "=head2 Caveats" section (only) within any of the three "=head1"
sections.

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

pod2usage(-verbose => 99, -sections => [
qw(DESCRIPTION DESCRIPTION/Introduction) ] );

This will print only the content of "=head1 DESCRIPTION" and the "=head2 Introduction"
sections, but no other "=head2", and no other "=head1" either.

"-output" handle
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").

"-input" handle
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).

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

use Pod::Find qw(pod_where);
pod2usage( -input => pod_where({-inc => 1}, __PACKAGE__) );

"-pathlist" string
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).

"-noperldoc"
By default, Pod::Usage will call perldoc when -verbose >= 2 is specified. This does
not work well e.g. if the script was packed with PAR. The -noperldoc option suppresses
the external call to perldoc and uses the simple text formatter (Pod::Text) to output
the POD.

"-perlcmd"
By default, Pod::Usage will call perldoc when -verbose >= 2 is specified. In case of
special or unusual Perl installations, the -perlcmd option may be used to supply the
path to a perl executable which should run perldoc.

"-perldoc" path-to-perldoc
By default, Pod::Usage will call perldoc when -verbose >= 2 is specified. In case
perldoc is not installed where the perl interpreter thinks it is (see Config), the
-perldoc option may be used to supply the correct path to perldoc.

"-perldocopt" string
By default, Pod::Usage will call perldoc when -verbose >= 2 is specified. The
-perldocopt option may be used to supply options to perldoc. The string may contain
several, space-separated options.

Formatting base class
The default text formatter is Pod::Text. The base class for Pod::Usage can be defined by
pre-setting $Pod::Usage::Formatter before loading Pod::Usage, e.g.:

BEGIN { $Pod::Usage::Formatter = 'Pod::Text::Termcap'; }
use Pod::Usage qw(pod2usage);

Pod::Usage uses Pod::Simple's _handle_element_end() method to implement the section
selection, and in case of verbosity < 2 it down-cases the all-caps headings to first
capital letter and rest lowercase, and adds a colon/newline at the end of the headings,
for better readability. Same for verbosity = 99.

Pass-through options
The following options are passed through to the underlying text formatter. 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 (using its embedded pod
       documentation) 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:

       •   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.

       •   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.

       •   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.

       •   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:

       •   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.

       •   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.

       •   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.

       •   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
           specifying -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)).

       •   If program usage has been explicitly requested by the user, it is often desirable to
           exit with a status of 1 (as opposed to 0) after issuing the user-requested usage
           message.  It is also desirable 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
       single number or a string makes it convenient to use as an innocent looking error message
       handling function:

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

           ## Parse options
           my %opt;
           GetOptions(\%opt, "help|?", "man", "flag1")  ||  pod2usage(2);
           pod2usage(1)  if ($opt{help});
           pod2usage(-exitval => 0, -verbose => 2)  if ($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 strict;
           use Pod::Usage qw(pod2usage);
           use Getopt::Long qw(GetOptions);

           ## Parse options
           my %opt;
           GetOptions(\%opt, "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".

   Scripts
       The Pod::Usage distribution comes with a script pod2usage which offers a command line
       interface to the functionality of Pod::Usage. See pod2usage.

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 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(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
       syntax 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"
       (perhaps by allowing a "-man" option). The following complete example uses Pod::Usage in
       combination with Getopt::Long to do all of these things:

           use strict;
           use Getopt::Long qw(GetOptions);
           use Pod::Usage qw(pod2usage);

           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 4

           =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 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");

       In the pathological case that a script is called via a relative path and the script itself
       changes the current working directory (see "chdir" in perlfunc) before calling pod2usage,
       Pod::Usage will fail even on robust platforms. Don't do that. Or use FindBin to locate the
       script:

           use FindBin;
           pod2usage(-input => $FindBin::Bin . "/" . $FindBin::Script);

AUTHOR

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

       Marek Rouchal <marekr@cpan.org>

       Brad Appleton <bradapp@enteract.com>

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

ACKNOWLEDGMENTS

       rjbs for refactoring Pod::Usage to not use Pod::Parser any more.

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