On Mar 26, 2010, at 7:10 PM, Raj Mathur wrote:
> On Friday 26 Mar 2010, Logu wrote:
>> I am trying to get the exit status of the first command on the pipe,
>> but I always get the exit status of the pipe reader.
>>
>> cat nofile; |sed -n '/abc/p'; echo "Error: $?"
>>
>> I tried this, but didnt work to my requirement
>>
>> { cat nofile; err=$?; } |sed -n '/abc/p'; echo "Error: $err"
>
> Two problems here:
>
> 1. The whole pipe executes in a subshell, so variables set in the pipe
> will not be visible in the calling shell.
>
> 2. The problem you have noted, viz getting the exit status of the
> first
> command in the pipe.
>
>> This is actually a simplified version of my requirement, any other
>> method to accomplish this efficiently?
>>
>> Two possible solution are
>> 1. Find the exit status first by executing the cat command and then
>> do the pipe again.
>> Problem: I actually have a command in place of cat which takes
>> long time and hence I can not execute it twice.
>>
>> 2. write the exit status to a file and use it further.
>> Problem: some how I feel there is a better way of doing without
>> writing the value to the disk.
>
> The second seems to be the best way of doing it. If you're sure
> there's
> nothing else being printed to STDERR, you could also output the exit
> status to STDERR and capture it later. Untested, but something like
> this could work:
>
> stat=`(( cat $file; echo $? >&2 ) | sed... > $anotherfile) 2>&1`
Thanks for your mail. I got a solution atleast this works for bash
http://tldp.org/LDP/abs/html/internalvariables.html#PIPESTATUSREF
The exit status of the first command is stored on ${PIPESTATUS[0]}
Regards
-logu
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