Bash help requested: Capturing command errors within pipes

[Daniel B. Thurman]

Daniel B. Thurman wrote:
> Steven W. Orr wrote:
>> On Thursday, Mar 19th 2009 at 14:11 -0000, quoth Daniel B. Thurman:
>>
>> =>S P Arif Sahari Wibowo wrote:
>> =>> On Thu, 19 Mar 2009, Daniel B. Thurman wrote:
>> =>> > How could one go about capturing command errors within pipes?
>> =>> =>> The variable $PIPESTATUS is just for that.
>> =>> =>I tried it, seems not to work.
>> =>
>> =>Try capturing a sed error when re1 or re2 has a bad regular
>> =>expression string.  I have not been able to catch the error.
>>
>> Sorry, but you'll have to supply something more specific. It's 
>> possible for a program to have an error but not return a proper exit 
>> status.
>>
>> But so far, my highly scientific test has revealed that all is good 
>> in pipe testing land in the Kingdom of Bash.
>>
>> 578 > true | false | true | true
>> 579 > echo ${PIPESTATUS[@]}
>> 0 1 0 0
>>   
>
> OK, I found out why I had a problem!
>
> I setup an intentional sed error:
> $ (re="-e '\'s/b/h/'"; echo "boo" | sed $re | echo "done"; echo 
> ${PIPESTATUS})
> done
> sed: -e expression #1, char 1: unknown command: `''
> 0
>
> Same thing but with @ pipe status expression
> $ (re="-e '\'s/b/h/'"; echo "boo" | sed $re | echo "done"; echo 
> ${PIPESTATUS[@]})
> done
> sed: -e expression #1, char 1: unknown command: `''
> 0 1 0
>
> My problem was that the last command was OK, of which
> PIPESTATUS was reporting, thus I was not properly capturing
> the exact status location where the error occurred!  duh!
>
> Your example showed me the way!
>
> Thanks!
> Dan
>
Oops, not the LAST command but the FIRST command, I think.
$PIPESTATUS is the same as $PIPESTATUS[0]

Dan