Learning Perl, 5th 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 already expanded it. This works even 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
$

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

But sometimes we end up with a pattern like *.pm inside our Perl program. Can we expand this pattern into the matching filenames without working very 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, just like the shell. And @pm_files gets the same list that we got before by using *.pm on the command line.

In fact, anything you can say on the command line, you can also 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 ...