repeated matches in grep

[Peter Saffrey]

I have seemingly bug-like behaviour from gnu grep version 2.3 and 2.4 for 
linux.

I'm trying to find all the instances of a word that contains 6 of the same
letter by grepping through /usr/dict/words.

this works:

grep '\(.\).*\1.*\1.*\1.*\1.*\1' /usr/dict/words

but this does not:

grep '\(.\)\(.*\1\)\{5\}' /usr/dict/words

Shouldn't they be equivalent?

In perl, the regular expression (.)(.*\1){5} which seems to be equivalent
gives the correct results.

I guess this may not be a failure of grep, but rather the regular
expression library... In any case. 

Cheers,

Peter

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