I really like Path::Class::Rule for searching the filesystem. Its author (David Golden) has recently been working on a faster replacement though (Path::Iterator::Rule) and your question has given me a chance to experiment with it...

use 5.010;
use strict;
use warnings;

use Path::Iterator::Rule;
use Path::Tiny;

# The directories we're looking in.
#
my @search_dirs = ('/home/tai/tmp');

# The regular expression we're searching for.
#
my $search_for = qr{foo};

"Path::Iterator::Rule"->add_helper(
    contents_match => sub {
        my $regexp = shift;
        sub {
            my $item = path(shift);
            return unless $item->is_file;
            $item->slurp_utf8 =~ $regexp;
        };
    },
);

"Path::Iterator::Rule"->add_helper(
    line_match => sub {
        my $regexp = shift;
        sub {
            my $item = path(shift);
            return unless $item->is_file;
            my $fh = $item->openr_utf8;
            while (my $line = <$fh>) {
                return 1 if $line =~ $regexp;
            }
            return;
        };
    },
);

my @matches = "Path::Iterator::Rule"
    -> new
    -> file
    -> name(qr{\.txt$})
    -> line_match($search_for)
    -> all(@search_dirs)
;

say for @matches;
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