Try:

chomp( my $content = <INPUT> ); # to get rid of a trailing linebreak.
if ( $content =~ m/^\Q$searchword\E$/ ) # escape/quote funny characters in $searchword.

Update:
The anchors   ^   and   $   match beginning and end of the string. I understand that's what you want.
If you want to match the word inside a longer string, go for ccn's proposal using the word boundary   \b   instead of the anchors.
See either   perldoc perlrequick, perldoc perlre or perldoc perlretut

Cheers, Sören