advanced grep question
Paul Howarth
paul at city-fan.org
Thu Feb 2 15:43:10 UTC 2006
Steven J Lamb wrote:
> what I am looking for is information on how to use grep in the following
> way. I want to do essentially this
>
> grep (string1|string2|string3) filename
>
> I would use this to search filename for either string1, string2 or
> string 3 instances
>
> I realize I could do the following but would like to use it as one grep
> statement as I believe it should be more efficient.
>
>> tmp;
>
> grep string1 filename >>tmp;
> grep string2 filename >>tmp;
> grep string3 filename >>tmp
>
> as this would be defined in a normal regular expression. grep claims to
> be able to use this functionality as best I can tell ... it is
> documented in the man page and it says
>
> Two regular expressions may be joined by the infix operator |; the
> resulting regular expression matches
> any string matching either subexpression.
>
> I have not been able to find an example of this anywhere and have tried
> several forms of the syntax but no luck. my command interpreter keeps
> trying to use the pipe instead of letting grep have it.
>
> any one have any thoughts
egrep 'string1|string2|string3' filename
Paul.
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