Section 12.2.  Globbing

12.2. 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 globbingthe 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? Surejust 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. The space between these two items inside the quoted string is significant since it separates two different items you want to glob.^[*] The reason this works as the shell does is that prior to Perl Version 5.6, the glob operator called /bin/csh^[] behind the scenes to perform the expansion. Because of this, globs were time-consuming and could break in large directories or in other cases. Conscientious Perl hackers avoided globbing in favor of directory handles, which we will discuss later in this chapter. However, if you're using a modern version of Perl, you should no longer be concerned about such things.

^[*] Windows users may be accustomed to using a glob of *.* to mean "all files," but that means "all files with a dot in their names," even in Perl on Windows.

^[] Or a valid substitute if a C-shell wasn't available.