Learning Perl, Fourth Edition

m// in List Context

When you use split, the pattern specifies the separator: the part that isn’t the useful data. Sometimes it’s easier to specify what you want to keep.

When a pattern match (m//) is used in a list context, the return value is a list of the memory variables created in the match or an empty list if the match failed:

    $_ = "Hello there, neighbor!";
    my($first, $second, $third) = /(\S+) (\S+), (\S+)/;
    print "$second is my $third\n";

This makes it easy to give the match variables easy-to-use names, and these names may persist past the next pattern match. (Because there’s no =~ in that code, the pattern matches against $_ by default.)

The /g modifier you first saw on s/// also works with m//, which lets it match at more than one place in a string. In this case, a pattern with a pair of parentheses will return a memory from each time it matches:

    my $text = "Fred dropped a 5 ton granite block on Mr. Slate";
    my @words = ($text =~ /([a-z]+)/ig);
    print "Result: @words\n";
    # Result: Fred dropped a ton granite block on Mr Slate

This is like using split inside out. Instead of specifying what we want to remove, we specify what we want to keep.

If there are more than one pair of parentheses, each match may return more than one string. Let’s say we have a string we want to read into a hash, like this:

    my $data = "Barney Rubble Fred Flintstone Wilma Flintstone";
    my %last_name = ($data =~ /(\w+)\s+(\w+)/g);

Each time the pattern matches, it returns a pair of memories. Those pairs of values ...