Check return code of piped command OR Export variable to parent shell

I just spent a day or more with a peer working the problem of "how do we get the return code of the first command in a series of piped commands in bash?"

The problem is: $? will hold the return code of the last command in the pipe sequence. We tried doing various things like ( foocmd ; export OUTERR=$?) | gzip... The problem with that is that, in bash, exported variables are not "global", so the value of $OUTERR is lost as soon as we hit the ). {}'s also did not work.

My partner's hack was to read stdout from foocmd into a variable, which he later cat'ed into gzip. Ick. Since we're dumping databases with foocmd, we're sure to run into architecture-dependent bash variable size limits, not to mention the RAM requirement of storing entire DB dumps into a variable.

As is usually the case, in the end we found that we'd spent so much time because we were going about it the wrong way, and we lacked the simple truth that would help us solve the problem efficiently.

${PIPESTATUS[@]} is an array similar to $?, except that it stores the return code of each component in a piped series. Thus, if we do this:

# /bin/false | tr x y | wc > /dev/null 2>&1

# echo ${PIPESTATUS[@]}

...we get as output...

1 0 0

...the first command, /bin/false returned "1", and the others returned "0" each.

Properly, we would test the value of each array element before considering the execution of the whole to be a success.

Now, that array will be overwritten/cleared the very next command, so the first thing we want to do is copy the array:

FOO_EXITCODE=("${PIPESTATUS[@]}")

So simple in the end.