Manpages - Pod_Usage.3perl

Pod::Usage - extracts POD documentation and shows usage information

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 );

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 and/or USAGE sections of the pod documentation are printed. If the value is 1, then the SYNOPSIS and/or USAGE sections, 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|ENVIRONMENT/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. This 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, this 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. This option may be used to supply options to perldoc. The string may contain several, space-separated options.

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 does not 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.

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});

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 is not 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);

This module is managed in a GitHub repository, https://github.com/Dual-Life/Pod-Usage Feel free to fork and contribute, or to clone and send patches!

Please use https://github.com/Dual-Life/Pod-Usage/issues/new to file a bug report. The previous ticketing system, https://rt.cpan.org/Dist/Display.html?Queue=Pod-Usage, is deprecated for this package.

More general questions or discussion about POD should be sent to the pod-people@perl.org mail list. Send an empty email to pod-people-subscribe@perl.org to subscribe.

Marek Rouchal <marekr@cpan.org>

Nicolas R <nicolas@atoomic.org>

Brad Appleton <bradapp@enteract.com>

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

Pod::Usage (the distribution) is licensed under the same terms as Perl.

Nicolas R (ATOOMIC) for setting up the Github repo and modernizing this package.

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.

Pod::Usage is now a standalone distribution, depending on Pod::Text which in turn depends on Pod::Simple.

Pod::Perldoc, Getopt::Long, Pod::Find, FindBin, Pod::Text, Pod::Text::Termcap, Pod::Simple