15.1.1. Problem

15.1.2. Solution

use Getopt::Std;

# -v ARG, -D ARG, -o ARG, sets $opt_v, $opt_D, $opt_o
getopt("vDo");              
# -v ARG, -D ARG, -o ARG, sets $args{v}, $args{D}, $args{o}
getopt("vDo", \%args);

getopts("vDo:");         # -v, -D, -o ARG, sets $opt_v, $opt_D, $opt_o
getopts("vDo:", \%args); # -v, -D, -o ARG, sets $args{v}, $args{D}, $args{o}

use Getopt::Long;

GetOptions( "verbose"  => \$verbose,     # --verbose
            "Debug"    => \$debug,       # --Debug
            "output=s" => \$output );    # --output=string or --output string

15.1.3. Discussion

Most traditional programs like ls and rm take single-character options (also known as flags or switches), such as -l and -r. In the case of ls -l and rm -r, the argument is Boolean: either it is present or it isn't. Contrast this with gcc -o compiledfile source.c, where compiledfile is a value associated with the option -o. We can combine Boolean options into a single option in any order. For example:

% rm -r -f /tmp/testdir

Another way of saying this is:

% rm -rf /tmp/testdir

use Getopt::Std;
getopts("o:");
if ($opt_o) {
    print "Writing output to $opt_o";
}

Both getopt and getopts can take a second argument, a reference to a hash. If present, option values are stored in $hash{X} instead of $opt_X:

use Getopt::Std;

%option = ( );
getopts("Do:", \%option);

if ($option{D}) {
    print "Debugging mode enabled.\n";
}

 # if not set, set output to "-".  opening "-" for writing
 # means STDOUT
 $option{o} = "-" unless defined $option{o};

print "Writing output to file $option{o}\n" unless $option{o} eq "-";
open(STDOUT, "> $option{o}")
     or die "Can't open $option{o} for output: $!\n";

Some programs' options you specify using full words instead of single characters. These options are (usually) indicated with two dashes instead of one:

% gnutar --extract --file latest.tar

The value for the - -file option could also be given with an equals sign:

% gnutar --extract --file=latest.tar

use Getopt::Long;

GetOptions( "extract" => \$extract,
            "file=s"  => \$file );

if ($extract) {
    print "I'm extracting.\n";
}

die "I wish I had a file" unless defined $file;
print "Working on the file $file\n";

If a key in the hash is just an option name, it's a Boolean option. The corresponding variable will be set to false if the option wasn't given, or to 1 if it was. Getopt::Long provides fancier options than just the Boolean and value of Getopt::Std. Here's what the option specifier can look like:

15.1.4. See Also