You can use regular expression capturing, and backreferences.

if( 
    $string =~ m/
                  \b([[:alpha:]]+)\b  # Match and capture word
                  .*?                 # Skip what you don't need
                  \b\1\b              # Match the captured word
                /x
  ) {
    print $1, "\n";
}
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Limitation: Words can contain only alpha characters. You could modify the expression: [[:alpha:]] so as to include what you might consider to be legal word characters, such as ' (apostrophe) and - (hyphen). I used the /x modifier to facilitate grouping the regular expression's sub-expressions into meaningful clusters so that it's easier to read.

Hope this helps!