The typical method is to dynamically build an alternation RE and let the RE engine do all the optimisation and hard work in lovingly hand optimised C. We use qr// so the RE is compiled once and avoid vast numbers of hash lookups, functionally useless variable assignments*, and RE compiles that you are doing above. As a general rule loops are great territory for optimisation due to the repeated execution of the loop code.

my @terms = qw( foo bar baz fool foolish );
my $re = join '|', map{quotemeta} sort {length($b)<=>length($a)}@terms
+;
$re = qr/($re)/;

while(<DATA>){
    my @matches = $_ =~ m/$re/g;
  next unless @matches;
    print "Got @matches\n"
}

__DATA__
Only a foobar foolish fool
skips the sort by length
Without this foo you look foolish
and may match short elements!
[download]

Hash lookup tables may still have a place to convert a matched value into something else. Here is a trivial example. Beware /i as you need to lc($1) and use all lowercase keys in %terms or you won't get a match/lookup.

my %terms = ( foo => 'FOO', bar => 'BAR' );
my $re = join '|', map{quotemeta} sort {length($b)<=>length($a)}keys %
+terms;
$re = qr/($re)/i;

while(<DATA>){
    s/$re/$terms{lc($1)}/g;
    print;
}
__DATA__
foo is a word
Bar ba blacksheep
[download]