That's just not correct.

#!/usr/bin/perl -w

use strict;

foreach ("WORDHERE", "stuffthenWORDHERE", "WORDHEREthenstuff",
        "stuffbeforeWORDHEREstuffafter", "wordhere", "no_word_here")
{
  print "$_: ";
  if($_ =~ /WORDHERE/gi)
  {
    print "matches";
  }
  else
  {
    print "doesn't match";
  }
  print "\n";
}
[download]

produces

WORDHERE: matches
stuffthenWORDHERE: matches
WORDHEREthenstuff: matches
stuffbeforeWORDHEREstuffafter: matches
wordhere: matches
no_word_here: doesn't match