1Pod::Usage(3pm) Perl Programmers Reference Guide Pod::Usage(3pm)
2
6 Pod::Usage, pod2usage() - print a usage message from embedded pod docu‐
7 mentation
8
10 use Pod::Usage
11 my $message_text = "This text precedes the usage message.";
13 my $exit_status = 2; ## The exit status to use
14 my $verbose_level = 0; ## The verbose level to use
15 my $filehandle = \*STDERR; ## The filehandle to write to
16 pod2usage($message_text);
18 pod2usage($exit_status);
20 pod2usage( { -message => $message_text ,
22 -exitval => $exit_status ,
23 -verbose => $verbose_level,
24 -output => $filehandle } );
25 pod2usage( -msg => $message_text ,
27 -exitval => $exit_status ,
28 -verbose => $verbose_level,
29 -output => $filehandle );
30 pod2usage( -verbose => 2,
32 -noperldoc => 1 )
33
35 pod2usage should be given either a single argument, or a list of argu‐
36 ments corresponding to an associative array (a "hash"). When a single
37 argument is given, it should correspond to exactly one of the follow‐
38 ing:
39 · A string containing the text of a message to print before printing
41 the usage message
42 · A numeric value corresponding to the desired exit status
44 · A reference to a hash
46 If more than one argument is given then the entire argument list is
48 assumed to be a hash. If a hash is supplied (either as a reference or
49 as a list) it should contain one or more elements with the following
50 keys:
51 "-message"
53 "-msg"
54 The text of a message to print immediately prior to printing the
55 program's usage message.
56 "-exitval"
58 The desired exit status to pass to the exit() function. This
59 should be an integer, or else the string "NOEXIT" to indicate that
60 control should simply be returned without terminating the invoking
61 process.
62 "-verbose"
64 The desired level of "verboseness" to use when printing the usage
65 message. If the corresponding value is 0, then only the "SYNOPSIS"
66 section of the pod documentation is printed. If the corresponding
67 value is 1, then the "SYNOPSIS" section, along with any section
68 entitled "OPTIONS", "ARGUMENTS", or "OPTIONS AND ARGUMENTS" is
69 printed. If the corresponding value is 2 or more then the entire
70 manpage is printed.
71 The special verbosity level 99 requires to also specify the -sec‐
73 tion parameter; then these sections are extracted (see Pod::Select)
74 and printed.
75 "-section"
77 A string representing a selection list for sections to be printed
78 when -verbose is set to 99, e.g. "NAME⎪SYNOPSIS⎪DESCRIPTION⎪VER‐
79 SION".
80 "-output"
82 A reference to a filehandle, or the pathname of a file to which the
83 usage message should be written. The default is "\*STDERR" unless
84 the exit value is less than 2 (in which case the default is "\*STD‐
85 OUT").
86 "-input"
88 A reference to a filehandle, or the pathname of a file from which
89 the invoking script's pod documentation should be read. It
90 defaults to the file indicated by $0 ($PROGRAM_NAME for users of
91 English.pm).
92 "-pathlist"
94 A list of directory paths. If the input file does not exist, then
95 it will be searched for in the given directory list (in the order
96 the directories appear in the list). It defaults to the list of
97 directories implied by $ENV{PATH}. The list may be specified either
98 by a reference to an array, or by a string of directory paths which
99 use the same path separator as $ENV{PATH} on your system (e.g., ":"
100 for Unix, ";" for MSWin32 and DOS).
101 "-noperldoc"
103 By default, Pod::Usage will call perldoc when -verbose >= 2 is
104 specified. This does not work well e.g. if the script was packed
105 with PAR. The -noperldoc option suppresses the external call to
106 perldoc and uses the simple text formatter (Pod::Text) to output
107 the POD.
108
110 pod2usage will print a usage message for the invoking script (using its
111 embedded pod documentation) and then exit the script with the desired
112 exit status. The usage message printed may have any one of three levels
113 of "verboseness": If the verbose level is 0, then only a synopsis is
114 printed. If the verbose level is 1, then the synopsis is printed along
115 with a description (if present) of the command line options and argu‐
116 ments. If the verbose level is 2, then the entire manual page is
117 printed.
118 Unless they are explicitly specified, the default values for the exit
120 status, verbose level, and output stream to use are determined as fol‐
121 lows:
122 · If neither the exit status nor the verbose level is specified, then
124 the default is to use an exit status of 2 with a verbose level of
125 0.
126 · If an exit status is specified but the verbose level is not, then
128 the verbose level will default to 1 if the exit status is less than
129 2 and will default to 0 otherwise.
130 · If an exit status is not specified but verbose level is given, then
132 the exit status will default to 2 if the verbose level is 0 and
133 will default to 1 otherwise.
134 · If the exit status used is less than 2, then output is printed on
136 "STDOUT". Otherwise output is printed on "STDERR".
137 Although the above may seem a bit confusing at first, it generally does
139 "the right thing" in most situations. This determination of the
140 default values to use is based upon the following typical Unix conven‐
141 tions:
142 · An exit status of 0 implies "success". For example, diff(1) exits
144 with a status of 0 if the two files have the same contents.
145 · An exit status of 1 implies possibly abnormal, but non-defective,
147 program termination. For example, grep(1) exits with a status of 1
148 if it did not find a matching line for the given regular expres‐
149 sion.
150 · An exit status of 2 or more implies a fatal error. For example,
152 ls(1) exits with a status of 2 if you specify an illegal (unknown)
153 option on the command line.
154 · Usage messages issued as a result of bad command-line syntax should
156 go to "STDERR". However, usage messages issued due to an explicit
157 request to print usage (like specifying -help on the command line)
158 should go to "STDOUT", just in case the user wants to pipe the out‐
159 put to a pager (such as more(1)).
160 · If program usage has been explicitly requested by the user, it is
162 often desireable to exit with a status of 1 (as opposed to 0) after
163 issuing the user-requested usage message. It is also desireable to
164 give a more verbose description of program usage in this case.
165 pod2usage doesn't force the above conventions upon you, but it will use
167 them by default if you don't expressly tell it to do otherwise. The
168 ability of pod2usage() to accept a single number or a string makes it
169 convenient to use as an innocent looking error message handling func‐
170 tion:
171 use Pod::Usage;
173 use Getopt::Long;
174 ## Parse options
176 GetOptions("help", "man", "flag1") ⎪⎪ pod2usage(2);
177 pod2usage(1) if ($opt_help);
178 pod2usage(-verbose => 2) if ($opt_man);
179 ## Check for too many filenames
181 pod2usage("$0: Too many files given.\n") if (@ARGV > 1);
182 Some user's however may feel that the above "economy of expression" is
184 not particularly readable nor consistent and may instead choose to do
185 something more like the following:
186 use Pod::Usage;
188 use Getopt::Long;
189 ## Parse options
191 GetOptions("help", "man", "flag1") ⎪⎪ pod2usage(-verbose => 0);
192 pod2usage(-verbose => 1) if ($opt_help);
193 pod2usage(-verbose => 2) if ($opt_man);
194 ## Check for too many filenames
196 pod2usage(-verbose => 2, -message => "$0: Too many files given.\n")
197 if (@ARGV > 1);
198 As with all things in Perl, there's more than one way to do it, and
200 pod2usage() adheres to this philosophy. If you are interested in see‐
201 ing a number of different ways to invoke pod2usage (although by no
202 means exhaustive), please refer to "EXAMPLES".
203
205 Each of the following invocations of "pod2usage()" will print just the
206 "SYNOPSIS" section to "STDERR" and will exit with a status of 2:
207 pod2usage();
209 pod2usage(2);
211 pod2usage(-verbose => 0);
213 pod2usage(-exitval => 2);
215 pod2usage({-exitval => 2, -output => \*STDERR});
217 pod2usage({-verbose => 0, -output => \*STDERR});
219 pod2usage(-exitval => 2, -verbose => 0);
221 pod2usage(-exitval => 2, -verbose => 0, -output => \*STDERR);
223 Each of the following invocations of "pod2usage()" will print a message
225 of "Syntax error." (followed by a newline) to "STDERR", immediately
226 followed by just the "SYNOPSIS" section (also printed to "STDERR") and
227 will exit with a status of 2:
228 pod2usage("Syntax error.");
230 pod2usage(-message => "Syntax error.", -verbose => 0);
232 pod2usage(-msg => "Syntax error.", -exitval => 2);
234 pod2usage({-msg => "Syntax error.", -exitval => 2, -output => \*STDERR});
236 pod2usage({-msg => "Syntax error.", -verbose => 0, -output => \*STDERR});
238 pod2usage(-msg => "Syntax error.", -exitval => 2, -verbose => 0);
240 pod2usage(-message => "Syntax error.",
242 -exitval => 2,
243 -verbose => 0,
244 -output => \*STDERR);
245 Each of the following invocations of "pod2usage()" will print the "SYN‐
247 OPSIS" section and any "OPTIONS" and/or "ARGUMENTS" sections to "STD‐
248 OUT" and will exit with a status of 1:
249 pod2usage(1);
251 pod2usage(-verbose => 1);
253 pod2usage(-exitval => 1);
255 pod2usage({-exitval => 1, -output => \*STDOUT});
257 pod2usage({-verbose => 1, -output => \*STDOUT});
259 pod2usage(-exitval => 1, -verbose => 1);
261 pod2usage(-exitval => 1, -verbose => 1, -output => \*STDOUT});
263 Each of the following invocations of "pod2usage()" will print the
265 entire manual page to "STDOUT" and will exit with a status of 1:
266 pod2usage(-verbose => 2);
268 pod2usage({-verbose => 2, -output => \*STDOUT});
270 pod2usage(-exitval => 1, -verbose => 2);
272 pod2usage({-exitval => 1, -verbose => 2, -output => \*STDOUT});
274 Recommended Use
276 Most scripts should print some type of usage message to "STDERR" when a
278 command line syntax error is detected. They should also provide an
279 option (usually "-H" or "-help") to print a (possibly more verbose)
280 usage message to "STDOUT". Some scripts may even wish to go so far as
281 to provide a means of printing their complete documentation to "STDOUT"
282 (perhaps by allowing a "-man" option). The following complete example
283 uses Pod::Usage in combination with Getopt::Long to do all of these
284 things:
285 use Getopt::Long;
287 use Pod::Usage;
288 my $man = 0;
290 my $help = 0;
291 ## Parse options and print usage if there is a syntax error,
292 ## or if usage was explicitly requested.
293 GetOptions('help⎪?' => \$help, man => \$man) or pod2usage(2);
294 pod2usage(1) if $help;
295 pod2usage(-verbose => 2) if $man;
296 ## If no arguments were given, then allow STDIN to be used only
298 ## if it's not connected to a terminal (otherwise print usage)
299 pod2usage("$0: No files given.") if ((@ARGV == 0) && (-t STDIN));
300 __END__
301 =head1 NAME
303 sample - Using GetOpt::Long and Pod::Usage
305 =head1 SYNOPSIS
307 sample [options] [file ...]
309 Options:
311 -help brief help message
312 -man full documentation
313 =head1 OPTIONS
315 =over 8
317 =item B<-help>
319 Print a brief help message and exits.
321 =item B<-man>
323 Prints the manual page and exits.
325 =back
327 =head1 DESCRIPTION
329 B<This program> will read the given input file(s) and do something
331 useful with the contents thereof.
332 =cut
334
336 By default, pod2usage() will use $0 as the path to the pod input file.
337 Unfortunately, not all systems on which Perl runs will set $0 properly
338 (although if $0 isn't found, pod2usage() will search $ENV{PATH} or else
339 the list specified by the "-pathlist" option). If this is the case for
340 your system, you may need to explicitly specify the path to the pod
341 docs for the invoking script using something similar to the following:
342 pod2usage(-exitval => 2, -input => "/path/to/your/pod/docs");
344 In the pathological case that a script is called via a relative path
346 and the script itself changes the current working directory (see
347 "chdir" in perlfunc) before calling pod2usage, Pod::Usage will fail
348 even on robust platforms. Don't do that.
349
351 Please report bugs using <http://rt.cpan.org>.
352 Brad Appleton <bradapp@enteract.com>
354 Based on code for Pod::Text::pod2text() written by Tom Christiansen
356 <tchrist@mox.perl.com>
357
359 Steven McDougall <swmcd@world.std.com> for his help and patience with
360 re-writing this manpage.
361perl v5.8.8 2001-09-21 Pod::Usage(3pm)