Learning Perl, Fourth Edition

Globbing

Normally, the shell expands any filename patterns on each command line into the matching filenames. This is called globbing . For example, if you give a filename pattern of *.pm to the echo command, the shell expands this list to a list of names that match:

    $ echo *.pm
    barney.pm dino.pm fred.pm wilma.pm
    $

The echo command doesn’t have to know anything about expanding *.pm because the shell has expanded it. This works for your Perl programs:

    $ cat >show-args
    foreach $arg (@ARGV) {
      print "one arg is $arg\n";
    }
    ^D
    $ perl show-args *.pm
    one arg is barney.pm
    one arg is dino.pm
    one arg is fred.pm
    one arg is wilma.pm
    $

show-args didn’t need to know anything about globbing—the names were already expanded in @ARGV.

Sometimes we end up with a pattern such as *.pm inside our Perl program. Can we expand this pattern into the matching filenames without working hard? Sure—just use the glob operator:

    my @all_files = glob "*";
    my @pm_files = glob "*.pm";

Here, @all_files gets all the files in the current directory, alphabetically sorted, and not including the files beginning with a period, like the shell. And @pm_files gets the same list as we got before by using *.pm on the command line.

Anything you can say on the command line, you can put as the (single) argument to glob, including multiple patterns separated by spaces:

    my @all_files_including_dot = glob ".* *";

Here, we’ve included an additional “dot star” parameter to get the filenames that begin with a dot as well as the ones that don’t. ...