7.2.36 Getopt::Std - Process Single-Character Options with Option Clustering

use Getopt::Std;

getopt('oDI');    # -o, -D & -I take arg.  Sets opt_* as a side effect.
getopts('oif:');  # -o & -i are boolean flags, -f takes an argument.
                  # Sets opt_* as a side effect.

The getopt() and getopts() functions give your program simple mechanisms for processing single-character options. These options can be clustered (for example, -bdLc might be interpreted as four single-character options), and you can specify individual options that require an accompanying argument. When you invoke getopt() or getopts(), you pass along information about the kinds of options your program expects. These functions then analyze @ARGV, extract information about the options, and return this information to your program in a set of variables. The processing of @ARGV stops when an argument without a leading "-" is encountered, if that argument is not associated with a preceding option. Otherwise, @ARGV is processed to its end and left empty.

For each option in your program's invocation, both getopt() and getopts() define a variable $opt_x where x is the option name. If the option takes an argument, then the argument is read and assigned to $opt_x as its value; otherwise, a value of 1 is assigned to the variable.

Invoke getopt() with one argument, which should contain all options that require a following argument. For example:

getopt('dV');

If your program is then invoked as:

myscr -bfd January -V 10.4

then these variables will be set in the program:

$opt_b = 1;
$opt_f = 1;
$opt_d = "January";
$opt_V = 10.4;

Space between an option and its following argument is unnecessary. The previous command line could have been given this way:

myscr -bfdJanuary -V10.4

In general, your program can be invoked with options given in any order. All options not "declared" in the invocation of getopt() are assumed to be without accompanying argument.

Where getopt() allows any single-character option, getopts() allows only those options you declare explicitly. For example, this invocation:

getopts('a:bc:');

legitimizes only the options -a, -b, and -c. The colon following the a and c means that these two options require an accompanying argument; b is not allowed to have an argument. Accordingly, here are some ways to invoke the program:

myscr -abc              # WRONG unless bc is really the argument to -a
myscr -a -bc            # WRONG, with same qualification
myscr -a foo -bc bar    # $opt_a = "foo"; $opt_b = 1; $opt_c = "bar"
myscr -bafoo -cbar      # same as previous

getopts() returns false if it encounters errors during option processing. However, it continues to process arguments and assign values as best it can to $opt_x variables. You should always check for errors before assuming that the variables hold meaningful values.

getopt() does not return a meaningful value.

Remember that both getopt() and getopts() halt argument processing upon reading an argument (without leading "-") where none was called for. This is not considered an error. So a user might invoke your program with invalid arguments, without your being notified of the fact. However, you can always check to see whether @ARGV has been completely emptied or not - that is, whether all arguments have been processed. If you're using the use strict pragma, which requires you to employ only lexical variables or else globals that are fully declared, you will have to use the double-colon package delimiter or else the use vars pragma. For example:

use strict;
use vars qw($opt_o $opt_i $opt_D);
use Getopt::Std;