matching an array of alternates

[Anonymous Monk]

Suppose I have an array @latin_am=("Ecuador","Mexico");
The actual array contains 10 countries.
I want to scan a text file for any line that matches /Ecuador/ or /Mexico/ or or any other country in the array.
What is the most efficient way of accomplishing this? Thanks very much.

[btrott]

Build a regular expression that will match those countries, then scan through the file and check each line against it:

    my $regex = join '|', @latin_am;
    while (<>) {
        print $1 if /$regex/;
    }

This reads from STDIN, so invoke it like this:

    % foo.pl file

[Zoogie]

Just wanted to point out that if the file you're searching has a lot of lines, you can gain some speed by adding the "o" option to the regex; i.e.:

    print $1 if /$regex/o;

This way, the regular expression only has to be compiled once.

- Zoogie

[takshaka]

The pipe-joined monolithic regex isn't terribly efficient.

The qr// approach described in perlfaq6 (that is, versions of perlfaq6 that ship with Perl 5.005 or later, but not the one on this site) is much faster.

my @regexes = map { qr/\Q$_/ } @latin_am;
while (<>) {
    for my $regex (@regexes) {
        if ($_ =~ $regex) {
            print;
            last;
        }
    }
}

[perlmonkey]

This should do the trick:

@latin_am=("Ecuador","Mexico");
$regex = join ("|", @latin_am);

open( FILE, 'input.txt' ) or die "input.txt: $!";
@lines = grep { /$regex/o } <FILE>;

@lines will hold all the lines of the file 'input.txt' that match any of the phrases in @latin_am