chen li am Dienstag, 26. September 2006 15:52:
> Hi all,
Hi chen
> I see some codes as following
>
> my $regexp= "(([gatc]{3})\\2{3,})";
Single quotes would make the double slash unnecessary:
my $regexp= '(([gatc]{3})\2{3,})';
[...]
> What is the meaning of {3,} of in \2{3,} ?
>
> I know \2 is a backreference here but not sure {3,}.
> I check the camel book and some perldoc but I can't
> find answer.
Check perldoc perlre, "Regular Expressions":
" The following standard quantifiers are recognized:
[...]
{n} Match exactly n times
{n,} Match at least n times
{n,m} Match at least n but not more than m times
"
"\2{3,}" in your regexp means that what "[gatc]{3}" matched should at least
match three times.
Dani
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