Pod::Usage(3) Perl Programmers Reference Guide Pod::Usage(3)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 );
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 corre
spond 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 sta
tus
A reference to a hash
If more than one argument is given then the entire argu
ment 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() func
tion. 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 print
ing the usage message. If the corresponding value is
0, then only the "SYNOPSIS" section of the pod docu
mentation is printed. If the corresponding value is 1,
then the "SYNOPSIS" section, along with any section
entitled "OPTIONS", "ARGUMENTS", or "OPTIONS AND ARGU
MENTS" 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 "\*STDOUT").
""-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 "ver
boseness": 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 other
wise.
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 out
put to a pager (such as more(1)).
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("$0: Too many files given.\n") if (@ARGV > 1);
Some user's however may feel that the above "economy of
expression" is not particularly readable nor consistent
and may instead choose to do something more like the fol
lowing:
use Pod::Usage;
use Getopt::Long;
## Parse options
GetOptions("help", "man", "flag1") || pod2usage(-verbose => 0);
pod2usage(-verbose => 1) if ($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 the section on "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 "SYNOPSIS" section and any "OPTIONS" and/or
"ARGUMENTS" sections to "STDOUT" and will exit with a sta
tus 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
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.
2001-02-22 perl v5.6.1 Pod::Usage(3)
