Regular Expressions

Regular Expressions

Perl is famous for its powerful regular expression support. We will use split with regex patterns and build pattern-matching subroutines.

Split with Regex

my @words = split(/\s+/, "hello   world   perl");
# ("hello", "world", "perl")

Building a Validator

You can write subroutines that check patterns manually:

sub is_digit_string {
    my ($str) = @_;
    my @chars = split("", $str);
    foreach my $ch (@chars) {
        if ($ch lt "0" or $ch gt "9") {
            return 0;
        }
    }
    return 1;
}

Grep and Map

grep filters a list, map transforms it:

my @nums = (1, 2, 3, 4, 5, 6);
my @evens = grep { $_ % 2 == 0 } @nums;   # (2, 4, 6)
my @doubled = map { $_ * 2 } @nums;         # (2, 4, 6, 8, 10, 12)

Your Task

Use grep to filter an array to only keep numbers greater than 3, then print each on its own line.