Regex match entire words only

Question

I have a regex expression that I'm using to find all the words in a given block of content, case insensitive, that are contained in a glossary stored in a database. It appears too be a little too inclusive. Here's my pattern:

/($word)/i

The problem is, if the word "Foo" is in the glossary then the first three letters of the word "Food" get matched. How can I modify my expression to match only the word "Foo" when it is a word at the beginning, middle, or end of a sentence?

Answer 1

Use word boundaries:

/\b($word)\b/i

Or if you're searching for "S.P.E.C.T.R.E." like in Sinan Ünür's example:

/(?:\W|^)(\Q$word\E)(?:\W|$)/i

Answer 2

Using \b can yield surprising results. You would be better off figuring out what separates a word from its definition and incorporating that information into your pattern.

#!/usr/bin/perl

use strict; use warnings;

use re 'debug';

my $str = 'S.P.E.C.T.R.E. (Special Executive for Counter-intelligence,
Terrorism, Revenge and Extortion) is a fictional global terrorist
organisation';

my $word = 'S.P.E.C.T.R.E.';

if ( $str =~ /\b(\Q$word\E)\b/ ) {
    print $1, "\n";
}

Output:

Compiling REx "\b(S\.P\.E\.C\.T\.R\.E\.)\b"
Final program:
   1: BOUND (2)
   2: OPEN1 (4)
   4:   EXACT  (9)
   9: CLOSE1 (11)
  11: BOUND (12)
  12: END (0)
anchored "S.P.E.C.T.R.E." at 0 (checking anchored) stclass BOUND minlen 14
Guessing start of match in sv for REx "\b(S\.P\.E\.C\.T\.R\.E\.)\b" against "S.P
.E.C.T.R.E. (Special Executive for Counter-intelligence,"...
Found anchored substr "S.P.E.C.T.R.E." at offset 0...
start_shift: 0 check_at: 0 s: 0 endpos: 1
Does not contradict STCLASS...
Guessed: match at offset 0
Matching REx "\b(S\.P\.E\.C\.T\.R\.E\.)\b" against "S.P.E.C.T.R.E. (Special Exec
utive for Counter-intelligence,"...
   0           |  1:BOUND(2)
   0           |  2:OPEN1(4)
   0           |  4:EXACT (9)
  14      |  9:CLOSE1(11)
  14      | 11:BOUND(12)
                                  failed...
Match failed
Freeing REx: "\b(S\.P\.E\.C\.T\.R\.E\.)\b"