Maybe I'm misunderstanding the problem ...

... but this works for me, if your "placeholder" is a variable starting with $ . 

> perl -de0
...
  DB<1> @a = qw(Russia Russia's Russias Russian)

  DB<2> $wordstem = "Russia"

  DB<3> x grep { /\bwordstem(s|\'s|n)?\b/i } @a
  empty array

  DB<4> x grep { /\b$wordstem(s|\'s|n)?\b/i } @a
0  'Russia'
1  'Russia\'s'
2  'Russias'
3  'Russian'

[download]

Cheers Rolf
(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery

In reply to Re: Regex: match a word stem plus an optional suffix from a group by LanX
in thread Regex: match a word stem plus an optional suffix from a group by element22

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