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corrupt

Member

Registered: 2007-06-25

Posts: 74

grep: how to match one letter in a string

How to find a string with exaclty one occurence of some letter?
For example that regular expresion must match "3434w3456" and not match "642w567w4".

thanks

icetonic

Member

From: Germany

Registered: 2008-10-21

Posts: 104

Re: grep: how to match one letter in a string

I doubt that you can express what you want as a regular expression... So I doubt grep can do this...

But I'm quite sure that sed can...

Unfortunately the only sed command I know and I ever needed is the replace command s/x/y/ ...

Procyon

Member

Registered: 2008-05-07

Posts: 1,819

Re: grep: how to match one letter in a string

Regex can do it with ^ inside brackets which negates it.
grep '^[^w]*w[^w]*$'

corrupt

Member

Registered: 2007-06-25

Posts: 74

Re: grep: how to match one letter in a string

thanks, Procyon.

Ramses de Norre

Member

From: Leuven - Belgium

Registered: 2007-03-27

Posts: 1,289

Re: grep: how to match one letter in a string

I doubt that you can express what you want as a regular expression... So I doubt grep can do this...

But I'm quite sure that sed can...

Both sed and grep use regular expressions so their are equally powerful, and since you can easily design a finite state automaton for the language the OP is trying to match, it is certainly a regular language.