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Learning Perl, 5th Edition
book

Learning Perl, 5th Edition

by Randal L. Schwartz, Tom Phoenix, brian d foy
June 2008
Beginner content levelBeginner
352 pages
11h 16m
English
O'Reilly Media, Inc.
Content preview from 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 ...

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Publisher Resources

ISBN: 9780596520106Supplemental ContentErrata Page