Split - Page 15

We briefly saw split earlier on in the chapter, where we used it to break up a string into a list of words. In fact, we only saw it in a very simple form. Strictly speaking, it was a bit of a cheat to use it at all. We didn't see it then, but split was actually using a regular expression to do its stuff!

Using split on its own is equivalent to saying:

split /\s+/, $_; 

which breaks the default string $_ into a list of substrings, using whitespace as a delimiter. However, we can also specify our own regular expression: perl goes through the string, breaking it whenever the regexp matches. The delimiter itself is thrown away.

For instance, on the UNIX operating system, configuration files are sometimes a list of fields separated by colons. A sample line from the password file looks like this:

 
kake:x:10018:10020::/home/kake:/bin/bash

To get at each field, we can split when we see a colon:

	#!/usr/bin/perl
	# split.plx
    use warnings;
    use strict;
    my $passwd =
	  "kake:x:10018:10020::/home/kake:/bin/bash";
    my @fields = split /:/, $passwd;
    print "Login name : $fields[0]\n";
    print "User ID : $fields[2]\n";
    print "Home directory : $fields[5]\n"; 

>perl split.plx
Login name : kake
User ID : 10018
Home directory : /home/kake
>

[Lines 5 and 6 above are one line. They have been split for formatting purposes.]

Note that the fifth field has been left empty. Perl will recognize this as an empty field, and the numbering used for the following entries takes account of this. So $fields[5] returns /home/kake, as we'd otherwise expect. Be careful though - if the line you are splitting contains empty fields at the end, they will get dropped.

Join

To do the exact opposite, we can use the join operator. This takes a specified delimiter and interposes it between the elements of a specified array. For example:

 
	#!/usr/bin/perl 

	# join.plx 
	use warnings;use strict;
    my $passwd = "kake:x:10018:10020::/home/
    kake:/bin/bash";my @fields
    = split /:/, $passwd;print "Login name :
    $fields[0]\n";print "User
    ID : $fields[2]\n";print "Home directory : $fields[5]\n";

	my $passwd2 = join "#", @fields;
    print "Original password : $passwd\n";
    print "New password : $passwd2\n"; 

>perl join.plx
Login name : kake
User ID : 10018
Home directory : /home/kake
Original password : kake:x:10018:10020::/home/kake:/bin/bash
New password : kake#x#10018#10020##/home/kake#/bin/bash
>

Changing Delimiters - Page 14
Beginning Perl
Transliteration - Page 16