Ah, so it's the loading of the entire file that's slowing me down.

That, and probably smartmatch too (depending on what it does...).

And you say that your and kcott's solutions don't avoid that

No. Just don't use smartmatch and first:

use strict;
use warnings;

my @strings = qw(
  foobarbaz111222333444
  barbazfoo111555666999
  bazfoobar999888777666
);

my $text = <<'END';
bdfjadslfjhasdjklfhjklashdflkjadshfjkladhfjkldhfljkafjadfdji
adlfjhdlsjkfuiowerfhwehrbeblbflasdfbhjkaldhqpqheuihfbdfkhyyy
qjdpdbnfdbjdfklbasjfbajksdbfjaksdbfjaksdfbjkasdfhydsfadfjyyy
END

$text x= 1_000_000;
$text .= "bazfoobar999888777666\n";

printf "text size: %d bytes (%.2f mb)\n",
  length($text), length($text) / ( 1024 * 1024 );

my $regex = join '|', map quotemeta, @strings;
$regex = qr/^($regex)$/m;

printf "found %s at %d\n", $1, $-[0] if $text =~ $regex;
[download]

That simulates your memory mapped file.