perl -nE '$count{$1}++ while /\b(the|hi|linux)\b/ig; END{say "$_ => $count{$_}" for keys %count}' filename.txt

##</code><code>##

#!/usr/bin/perl

open $fh, '<', $ARGV[0] or die $!;

while( <$fh> ) {
  $count{$1}++ while /\b(the|hi|linux)\b/ig;
}

print "$_ => $count{$_}\n" for keys %count;