Which can probably be further reduced to: 
$ cat 1078350.in
12-12
12-12-12
12-13-12-13
12-12-13-13
12-13-13-14
$ perl -pe '1 while s/(\d\d)(.*?)(?:-\1)/$1$2/g' 1078350.in
12
12
12-13
12-13
12-13-14

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In reply to Re^3: How can I reduce this with a REGEX? by hazylife
in thread How can I reduce this with a REGEX? by misterperl

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