grep -q VS. grep > /dev/null

[Paul Mooring]

As a `grep -q` user I can confirm that modern Solarises and osx also
support it.


On Wed, May 28, 2014 at 11:19 PM, der.hans <PLUGd at lufthans.com> wrote:

> Am 28. Mai, 2014 schwätzte Bryan O'Neal so:
>
> moin moin Bryan,
>
> because you're weird :). Or maybe that's Al,
> http://www.youtube.com/watch?v=JUQDzj6R3p4 :).
>
> Not every grep supports -q, but I don't know if that's the case for
> current releases. GNU grep has supported it for years and years. Looks
> like FreeBSD has for at least a few major releases, so also for years and
> years.
>
> AIX, Solaris, etc. probably don't, but you should install GNU grep, GNU
> date, etc. on those anyway :).
>
> [[ ]] vs [ ] is just for extra emphasis :). Or maybe... [[ ]] is for
> compound commands and [ ] is for test. Both use conditional expressions.
>
> The compound command, [[ ]], allows extra operators.
>
> == and != allow glob pattern matching:
>
> $ ( fred=anke; if [[ $fred == *ke ]] ; then echo $fred; fi )
> anke
> $
>
> $ ( fred=anke; if [ $fred == *ke ] ; then echo $fred; fi )
> $
>
> $ ( fred=anke; if [[ $fred == [:alpha:]?ke ]] ; then echo $fred; fi )
> anke
> $
>
> =~ allows regex pattern matching:
>
> $ ( fred=anke; if [[ $fred == [:alpha:]*ke ]] ; then echo $fred; fi )
> anke
> $
>
> Hmm, cool. According to bash(1), "If the regular expression is
> syntactically incorrect, the conditional expression's return value is 2."
>
> Note that the patterns to be matched must be on the right hand side of the
> operator.
>
> Now I need to make time to update my class materials as I just realized
> there's a dearth of references to Weird Al :).
>
> ciao,
>
> der.hans
>
>
>  So I had a coworker ask me why I always do
>> echo $foo | grep $bar > /dev/null
>> if [[ $? -eq 0]] then; ....
>>
>> Instead of just using greps quiet option. And I remember their being
>> some definite bug with -q and checking return codes but for the life
>> of me I can not recall it right now.  Just like I can not recall why I
>> use [[ ]] insted of just [ ]. Their was a reason I switched at some
>> point but can not recall what it is.
>> It could have been somthing  with egrep or using peal regex with grep
>> but honestly I can not recall...
>>
>> Thus I am here to ask you, my fellow bash geeks, what what that reason!
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> --
> #  http://www.LuftHans.com/        http://www.LuftHans.com/Classes/
> #  "It's not that I'm so smart, it's just that I stay with problems
> longer."
> #  -- Albert Einstein
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-- 
Paul Mooring
Operations Engineer
Chef
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