I recommend to use ${^MATCH}.

Always use the /p regex modifier when using  ${^MATCH} and friends. The use of  ${^MATCH} may appear to work without the /p modifier, but this is only fortuitous.

Quoth perlvar (emphasis added):

${^MATCH}
This is similar to $& ($MATCH) except that it does not incur the performance penalty associated with that variable, and is only guaranteed to return a defined value when the pattern was compiled or executed with the "/p" modifier.

In reply to Re^2: Regex: Extracting the case insensitive string and printing on the output by AnomalousMonk
in thread Regex: Extracting the case insensitive string and printing on the output by rockstar99

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