Re: grep: echo -en "AB\nA B\n" | egrep 'A?B'

[John Cowan]

p.p. scripsit:

> if I do
> 
> echo -en "AB\nA B\n" | egrep 'A?B'
> 
> the result is
> AB
> A B
> 
> while, as I understand it, the second line containing the space should not 
> match.
> 
> Is this a bug in grep or in my understanding of regular expressions?

The latter.

Your pattern says to match an optional A followed by a B.  The first
line has an A followed by a B, so it matches; the second line has a B,
so it too matches.  The presence of an A on the second line is irrelevant.

You may want to wrap your pattern in ^ and $ to force it to match the
whole line.

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