My Perl-fu is non-existent but this caught my eye in another web search I was doing. I propose the following, non-golf, trivial method which does not require backreferencing;

([aA]{2}|[bB]{2}|[cC]{2}|[dD]{2}|[eE]{2}|[fF]{2}|[gG]{2}|[hH]{2}|[iI]{2}|[jJ]{2}|[kK]{2}|[lL]{2}|[mM]{2}|[nN]{2}|[oO]{2}|[pP]{2}|[qQ]{2}|[rR]{2}|[sS]{2}|[tT]{2}|[uU]{2}|[vV]{2}|[wW]{2}|[xX]{2}|[yY]{2}|[zZ]{2})

Needless to say, yikes.

In reply to Re: Using regex to match double letters, and only double letters by Anonymous Monk
in thread Using regex to match double letters, and only double letters by Anonymous Monk

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