Pod::Usage
Pod::Usage(3) Perl Programmers Reference Guide Pod::Usage(3)
NAME
Pod::Usage, pod2usage() - print a usage message from embedded pod docu-
mentation
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 );
ARGUMENTS
pod2usage should be given either a single argument, or a list of argu-
ments corresponding to an associative array (a "hash"). When a single
argument is given, it should correspond to exactly one of the follow-
ing:
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:
"-message"
"-msg"
The text of a message to print immediately prior to printing the
program's usage message.
"-exitval"
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"
The desired level of "verboseness" to use when printing the usage
message. If the corresponding 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.
"-output"
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 "\*STD-
OUT").
"-input"
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).
"-pathlist"
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).
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 argu-
ments. 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 fol-
lows:
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 conven-
tions:
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 expres-
sion.
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 specifying -help on the command line)
should go to "STDOUT", just in case the user wants to pipe the out-
put 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 message. 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 single number or a string makes it
convenient to use as an innocent looking error message handling func-
tion:
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 see-
ing a number of different ways to invoke pod2usage (although by no
means 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 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 "SYN-
OPSIS" section and any "OPTIONS" and/or "ARGUMENTS" sections to "STD-
OUT" 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 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 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");
AUTHOR
Please report bugs using <http://rt.cpan.org>.
Brad Appleton <bradapp@enteract.com>
Based on code for Pod::Text::pod2text() written by Tom Christiansen
<tchrist@mox.perl.com>
ACKNOWLEDGEMENTS
Steven McDougall <swmcd@world.std.com> for his help and patience with
re-writing this manpage.
perl v5.8.6 2001-09-21 Pod::Usage(3)
