Actually, if $pre, $searchTerm and $post are text rather than regexp patterns, ...

Actually, if $pre contains anything that would involve a variable-length match, it just won't work with the look-behind operator: 

perl -e '$pre="x+"; $_="xxFindme"; print "found" if(/(?<=$pre)Findme/)
+'

# dies with the message:

Variable length lookbehind not implemented in regex; marked by <-- HER
+E
 in m/(?<=x+)Findme <-- HERE / at -e line 1.

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That is, the regex quantifiers "*", "?", "+" and "{n,m}" cannot be used as such when doing a look-behind (though they will work with look-ahead). If the OP's $pre might ever contain one of these things, putting \Q...\E around it in the regex -- treating them as literals -- will at least make sure the script doesn't crash. -- update: and as ikegami explains below, there's a better way to handle this

(I'm sure ikegami knows this already, but it might not have been clear to mwunderlich or other readers.)

In reply to Re^2: Using lookaround with variables by graff
in thread Using lookaround with variables by mwunderlich

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