usage.pm

Astercon2 开源软交换 2.2.0

#############################################################################
# Pod/Usage.pm -- print usage messages for the running script.
#
# Copyright (C) 1996-2000 by Bradford Appleton. All rights reserved.
# This file is part of "PodParser". PodParser is free software;
# you can redistribute it and/or modify it under the same terms
# as Perl itself.
#############################################################################

package Pod::Usage;

use vars qw($VERSION);
$VERSION = 1.33;  ## Current version of this package
require  5.005;    ## requires this Perl version or later

=head1 NAME

Pod::Usage, pod2usage() - print a usage message from embedded pod documentation

=head1 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  )

=head1 ARGUMENTS

B<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:

=over 4

=item *

A string containing the text of a message to print I<before> printing
the usage message

=item *

A numeric value corresponding to the desired exit status

=item *

A reference to a hash

=back

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:

=over 4

=item C<-message>

=item C<-msg>

The text of a message to print immediately prior to printing the
program's usage message. 

=item C<-exitval>

The desired exit status to pass to the B<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.

=item C<-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 L<Pod::Select>)
and printed.

=item C<-section>

A string representing a selection list for sections to be printed
when -verbose is set to 99, e.g. C<"NAME|SYNOPSIS|DESCRIPTION|VERSION">.

=item C<-output>

A reference to a filehandle, or the pathname of a file to which the
usage message should be written. The default is C<\*STDERR> unless the
exit value is less than 2 (in which case the default is C<\*STDOUT>).

=item C<-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 C<$0> (C<$PROGRAM_NAME> for users of F<English.pm>).

=item C<-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 C<$ENV{PATH}>. The list may be specified either by a reference
to an array, or by a string of directory paths which use the same path
separator as C<$ENV{PATH}> on your system (e.g., C<:> for Unix, C<;> for
MSWin32 and DOS).

=item C<-noperldoc>

By default, Pod::Usage will call L<perldoc> when -verbose >= 2 is
specified. This does not work well e.g. if the script was packed
with L<PAR>. The -noperldoc option suppresses the external call to
L<perldoc> and uses the simple text formatter (L<Pod::Text>) to 
output the POD.

=back

=head1 DESCRIPTION

B<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:

=over 4

=item *

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.

=item *

If an exit status I<is> specified but the verbose level is I<not>, then the
verbose level will default to 1 if the exit status is less than 2 and
will default to 0 otherwise.

=item *

If an exit status is I<not> specified but verbose level I<is> given, then
the exit status will default to 2 if the verbose level is 0 and will
default to 1 otherwise.

=item *

If the exit status used is less than 2, then output is printed on
C<STDOUT>.  Otherwise output is printed on C<STDERR>.

=back

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:

=over 4

=item *

An exit status of 0 implies "success". For example, B<diff(1)> exits
with a status of 0 if the two files have the same contents.

=item *

An exit status of 1 implies possibly abnormal, but non-defective, program
termination.  For example, B<grep(1)> exits with a status of 1 if
it did I<not> find a matching line for the given regular expression.

=item *

An exit status of 2 or more implies a fatal error. For example, B<ls(1)>
exits with a status of 2 if you specify an illegal (unknown) option on
the command line.

=item *

Usage messages issued as a result of bad command-line syntax should go
to C<STDERR>.  However, usage messages issued due to an explicit request
to print usage (like specifying B<-help> on the command line) should go
to C<STDOUT>, just in case the user wants to pipe the output to a pager
(such as B<more(1)>).

=item *

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.

=back

B<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 B<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, I<there's more than one way to do it>, and
B<pod2usage()> adheres to this philosophy.  If you are interested in
seeing a number of different ways to invoke B<pod2usage> (although by no
means exhaustive), please refer to L<"EXAMPLES">.

=head1 EXAMPLES

Each of the following invocations of C<pod2usage()> will print just the
"SYNOPSIS" section to C<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 C<pod2usage()> will print a message
of "Syntax error." (followed by a newline) to C<STDERR>, immediately
followed by just the "SYNOPSIS" section (also printed to C<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 C<pod2usage()> will print the
"SYNOPSIS" section and any "OPTIONS" and/or "ARGUMENTS" sections to
C<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 C<pod2usage()> will print the
entire manual page to C<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});

=head2 Recommended Use