m/$keyword/
is wrong. You need to escape special characters. A simple way of doing this is
m/\Q$keyword/

my $pattern = join('|', @keywords );
has the same problem. Use
my $pattern = join('|', map quotemeta, @keywords);
instead.

If the list of words is long, you can speed things up a lot by using Regexp::List:
my $pattern = Regexp::List->new->list2re(@keywords);

All together, we get: 

use Regexp::List ();

my @keywords = ("keyword1", "keyword2", "keyword3");

my $pattern = Regexp::List->new->list2re(@keywords);
#my $pattern = join('|', map quotemeta, @keywords);  # Alternative

while (<SEARCHFILE>) {
   if ($_ =~ $pattern) {  # or just: if (/$pattern/) {
      print $_;           # or just:    print;
   }
}

[download]

In reply to Re^2: searching for keywords by ikegami
in thread searching for keywords by Anonymous Monk

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