Re: Problems using + with -f <file>

[Julian Foad]

Gert Jan van Loo wrote:
[...]
> My pattern file contains (among other lines):
> Input [a-zA-Z0-9_]+ is unused
>  
> If I use "grep -f <patternfile> <source>" The patterns are NOT found 
> If I use "egrep -f <patternfile> <source>" The patterns ARE found
>  
> If I change my pattern file to:
> Input [a-zA-Z0-9_]\+ is unused
> Now using "grep -f <patternfile> <source>" The patterns ARE found.
> Now using "egrep -f <patternfile> <source>" The patterns are NOT found.
>
> egrep seems to do the right thing. 
> I thought "[a-zA-Z0-9_]+" is part of the standard grep.
> Even if it is not why does \+ suddenly work? 

All of this is working as intended, and as documented.  GNU "grep" uses BRE 
syntax, but it has exactly the same ERE capabilities as "egrep".  Those 
capabilities are accessed by escaping ERE characters with "\" to give them 
their special meaning.

- Julian