Jon Bjornstad

NAME

Getopt::Easy - parses command line options in a simple but capable way.

SYNOPSIS

  use Getopt::Easy;

  get_options "v-verbose  f-fname=  D-debug=uSX",
              "usage => "usage: prog [-v] [-f fname] [-D [uSX]] [-H]",
              "H";

  print "reading $O{fname}\n" if $O{verbose};
  print "SQL: $sql\n" if $O{debug} =~ /S/;

DESCRIPTION

Perl puts the command line parameters in the array @ARGV allowing the user to examine and manipulate it like any other array. There is a long tradition of putting optional single character flags (preceded by a dash) in front of other parameters like so:

  % ls -ltr *.h *.c
  % tar -tvf all.tar
  % ps -ax -U jsmith

Many Getopt::* modules exist to help with the parsing of these flags out of @ARGV. For the author, Getopt::Std was visually too cryptic and Getopt::Long was too large and complex for most normal applications. Getopt::Easy is small, easy to understand, and provides a visual clarity.

There are two things exported: get_options() and %O.

get_options has 1 required parameter and 2 optional ones. The first is a string describing the kind of options that are expected. It is a space separated list of terms like this:

  get_options "v-verbose   f-fname=";

If the -v option is given on the command line %O{verbose} will be set to 1 (true). If the -f option is given then another argument is expected which will be assigned to $O{fname}.

Before parsing @ARGV, $O{verbose} will be initialized to 0 (false) and $O{fname} to "" (unless they already have a value).

If you give an unknown option get_options() will complain and exit:

  % prog -vX
  unknown option: -X
  %

These conventions are implemented by Getopt::Easy:

  • The options can come in any order.

  • Multiple boolean options can be bundled together.

  • A command line argument of '--' will cause argument parsing to stop so you can parse the rest of the options yourself.

  • Parsed arguments are removed from @ARGV.

These invocations are equivalent:

  % prog -v -f infile
  % prog -f infile -v     # different order
  % prog -v -finfile
  % prog -vf infile
  % prog -vfinfile

This shows that the space between -f and infile is optional and that you can bundle -f with -v but -f must be the last option in the bundle.

The optional second parameter to get_options() is a usage message to be printed when an illegal option is given.

  get_options "v-verbose   f-fname=",
              "usage: prog [-v] [-f fname]";

Now if an unknown option is given, the same error message will be printed, as above, followed by the usage message.

  % prog -vX
  unknown option: -X
  usage: prog [-v] [-f fname]
  %

HELP

Sometimes the usage message is not enough and the user needs more detailed and elaborate help. This is where the 3rd optional parameter comes in.

  get_options "v-verbose   f-fname=",
              "usage: prog [-v] [-f fname] [-H]",
              "H";

Giving the -H option will cause the POD for the module to be echoed to STDOUT - as if the user had typed 'perldoc prog'. See 'perldoc perlpod'.

DEBUGGING

There are various ways to implement a debugging option:

GOOD:

  get_options "d-debug";

  print "val = $val\n" if $O{debug};

BETTER:

  get_options "d-debug=";

  print "SQL = $sql\n" if $O{debug} >= 2;
  print "val = $val\n" if $O{debug} >= 3;

With this method there are various levels of debugging. Unfortunately, they often end up ranging from 'not enough' to 'too much' :(.

BEST:

  get_options "d-debug=eSvL";

  print "SQL = $sql\n" if $O{debug} =~ /S/;
  print "val = $val\n" if $O{debug }=~ /v/;
 

With this kind of term the letters after the equal sign '=' are the debugging options that are valid. Now the user can choose exactly what kind of debugging output they wish to see.

  % prog -d SL

Giving an illegal debugging option will result in an error message:

  % prog -deXSf
  for -d: illegal options: Xf, valid ones are: eSvL
  %

ACCESS ELSEWHERE

If you want access to the %O hash from other files simply put:

  use Getopt::Easy;

at the top of those files; the %O hash will again be exported into the current package. You need to have:

  get_options ...;

only once in the main file before anyone needs to look at the %O hash.

STRICT

It is easy to misspell a key for the %O hash. Tie::StrictHash can help with this:

  use GetOpt::Easy;
  use Tie::StrictHash;

  get_options "v-verbose  f-fname=";
  strict_hash %O;

  print "file name is $O{filename}\n";

This will give a fatal error message:

  key 'filename' does not exist at prog line 6

SEE ALSO

Config::Easy allows configuration file entries to be overidden with command line arguments.

Tie::StrictHash protects against misspelling of key names.

Date::Simple is an elegant way of dealing with dates.

AUTHOR

Jon Bjornstad <jon@icogitate.com>