[aklug] Re: Q for grep geeks

On Tuesday 26 August 2008 21:46:20 bryanm@acsalaska.net wrote:
> How can I match a doubled character, like the "ll" in sallied?
> I tried .{2} with egrep, but that just reduces to .. (any two
> characters).
>
> --
> Bryan Medsker
> bryanm@acsalaska.net

Use a back reference:

james@Samoa:~$ echo "sallied" | egrep -o ll
ll
james@Samoa:~$ echo "sallied" | egrep -o [[:alpha:]]{2}
sa
ll
ie
james@Samoa:~$ echo "sallied" | egrep -o "([[:alpha:]]+)\\1"
ll
james@Samoa:~$ echo "taffy" | egrep -o "([[:alpha:]]+)\\1"
ff
james@Samoa:~$ echo "f&&der" | egrep -o "(.+)\\1"
&&
james@Samoa:~$ echo "sallied" | egrep -o "(.+)\\1"
ll
                                              
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Received on Tue Aug 26 22:05:07 2008