Perl provides a rich language for searching for patterns within strings via its Regular Expression engine.

perldoc perlre
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This will give you way more info than you can absorb quickly. Now, based on your original post, you want to iterate over an array and check each element for a pattern (in this case, a string) and do something each time you find a match.

for my $line (@input) {
    if ($line =~ /$pattern/) {
        # Do something
        print "$line contains $pattern\n";
    }
}
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If you just want to get a count of lines that contain $pattern, Perl has a grep function (see perldoc -f grep for more on grep). It returns a list of matches based on some test. When evaluated in scalar context, the length of that list, or the number of matches, is returned.

my $match_cnt = grep { $_ =~ /$pattern/ } @input;
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With Perl, there is always more that one way to do things, but some are obviously better and more appropriate based on your needs.