Re: [MLUG] basic Unix pipe/exit code problem

[Mike Miller <EMAIL:PROTECTED>]

On Sat, 5 Mar 2005, Scott Hussey wrote:

> On Thu, 3 Mar 2005 12:24:49 -0600, Mark Rages <EMAIL:PROTECTED> wrote:
>> I have reduced my problem to this:
>>
>> ( /bin/false | gzip > /dev/null ) || echo fail
>>
>> I want it to echo "fail" because /bin/false gives a nonzero exit code.
>>  But it doesn't.  What am I missing?
>
> Google "PIPESTATUS" or search for it in the bash man page.
>
>       PIPESTATUS
>              An  array  variable (see Arrays below) containing a list of exit
>              status values from the processes in  the  most-recently-executed
>              foreground pipeline (which may contain only a single command).
>
>
> Scott-Husseys-Computer:~/dev/html scott$ false | gzip > /dev/null
> Scott-Husseys-Computer:~/dev/html scott$ echo ${PIPESTATUS[*]}
> 1 0


There it is!  So you can do things like this in a script:

#!/usr/bin/bash
false | sort | uniq | grep 1 | gzip | > /dev/null
echo ${PIPESTATUS[*]}

and it will return this:

1 0 0 1 0 0

Or, Mark could just look at PIPESTATUS[0] to see the exit status of the 
first command in the pipe.  I don't know bash so well, but something like 
this pseudocode:

if PIPESTATUS[0]==1 then
   echo "backup failed" | mail mark
fi

Would that work?

Mike
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