Pod::Usage(3p) Perl Programmers Reference Guide Pod::Usage(3p)NAME
Pod::Usage, pod2usage() - print a usage message from embed-
ded 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 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"
"-msg"
The text of a message to print immediately prior to
printing the program's usage message.
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"-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.
The special verbosity level 99 requires to also specify
the -section parameter; then these sections are
extracted (see Pod::Select) and printed.
"-section"
A string representing a selection list for sections to
be printed when -verbose is set to 99, e.g.
"NAME|SYNOPSIS|DESCRIPTION|VERSION".
"-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 direc-
tory 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 refer-
ence 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
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simple text formatter (Pod::Text) to output the POD.
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 other-
wise.
+ 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.
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+ 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 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 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("$0: Too many files given.\n") if (@ARGV > 1);
Some user's however may feel that the above "economy of
expression" is not particularly readable nor consistent and
may instead choose to do something more like the following:
use Pod::Usage;
use Getopt::Long;
## Parse options
GetOptions("help", "man", "flag1") || pod2usage(-verbose => 0);
pod2usage(-verbose => 1) if ($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 seeing a number of different ways to invoke
pod2usage (although by no means exhaustive), please refer to
"EXAMPLES".
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Pod::Usage(3p) Perl Programmers Reference Guide Pod::Usage(3p)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 "ARGU-
MENTS" sections to "STDOUT" and will exit with a status of
1:
pod2usage(1);
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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 com-
plete 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__
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=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 speci-
fied 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 rela-
tive 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.
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Pod::Usage(3p) Perl Programmers Reference Guide Pod::Usage(3p)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 v5.8.8 2005-02-05 8
