% cat 986735.pl
#!/usr/bin/env perl
use Modern::Perl;
use Benchmark qw(:all);

my @words = split /\s+/, `cat bigfile`; #8.5MB file
say scalar @words, " words in bigfile"; #1.3M words
my $match = 'professional'; # appears 16 times scattered through bigfile

cmpthese( 10, {
        'hash it' => \&hashit,
        'grep it' => \&grepit,
        'first it' => \&firstit,
});

sub hashit {
    my %h;
    @h{@words} = ();
    my $exists = exists $h{$match};
}

sub grepit {
    my $exists = grep { $_ eq $match } @words;
}

sub firstit {
    use List::Util 'first';
    my $exists = first { $_ eq $match } @words;
}
 % perl 986735.pl
1293687 words in bigfile
           Rate  hash it  grep it first it
hash it  3.33/s       --     -43%     -89%
grep it  5.80/s      74%       --     -81%
first it 29.8/s     795%     413%       --