grep question: either of 2 patterns?

[ken at kg293.net (Ken Gosier)]

Many thanks, this totally hit the spot. :-) Interestingly, /usr/bin/grep
on my (Solaris) machine doesn't list -[eE] as options, but they are
available with /usr/xpg4/bin/grep. I do have egrep, which I hadn't heard
of before, thus explaining my pretty basic question. :-P Anyways, thanx
again for the help!



Chris Devers said:
> On Tue, 2 Sep 2003, Ken Gosier wrote:
>
>> I want to use grep to match on lines in a file that begin with either
>> of 2 patterns. As far as I understand regex's, I should use ^(...|...)
>> to do this, as in:
>>
>> grep ^(fee|fie) junk.txt
>
> Tried egrep yet?
>
> On many systems, grep, egrep, and fgrep are the same binary (they might
> or might not be symlinks or hard links to each other, but the files are
> often identical).
>
> However, when this binary is invoked as egrep, you get extended
> matching.
>
> Otherwise, I think you need the -E flag.
>
> So:
>
>     egrep '^(fee|fie)' junk.txt
>
>     grep -E '^(fee|fie)' junk.txt
>
> Both should work identically.
>
>> Obviously this won't work b/c there are some characters there that are
>> meaningful to the shell. According to man grep, I should enclose my
>> pattern in single quotes to get around this:
>>
>> grep '^(fee|fie)' junk.txt
>>
>> However, this produces no lines of output (even though I know both
>> patterns are there).
>
> Because with regular grep, you're not using the extended metacharacter
> set, so the command is looking for the literal pattern (or something
> close to it anyway).
>
> But you're right, you do need to wrap any moderately fancy patterns in
> single or double quotes to protect that pattern from the shell.
>
>
> Clearer?
>
>
>
> --
> Chris Devers      cdevers at pobox.com
> http://devers.homeip.net:8080/blog/
>
> pun moratorium, n.
> The doomed campaign to deoxymoronize computer humor.
>
> In particular, the vain attempt to demonstrate that plays on words such
> as RISC and UNIX are unfunny if the player is unaware of their
> historically built-in playfulness. Other puns assinorum deserving a
> well-earned retirement relate PARADIGM, Paradise, and ten sents in
> boringly obvious ways: "Paradigms Lost and Regained," "Brother, can you
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> bankrupt: "Cache-only memory, no checks." Be assured, too, that every
> known C homophone has had its weary, C-sick day at the C-Users
> Journal's annual C-pun contest: C-through UNIX, C'est C Bon, Holy C,
> Proficient C, Vitamin C, O say can you C? e = mC^2, Variations in C, C-C
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> nau-C-am.
>
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>
>     -- from _The Computer Contradictionary_, Stan Kelly-Bootle, 1995
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-- 
Ken Gosier
ken at kg293.net
ken_gosier at yahoo.com