On a bash command line in Ubuntu 14.04 :
echo "z" | grep -e 'x' ; echo $PIPESTATUS
always displays 0, even though, obviously, there's no "x" in "z". But:
echo "z" > /tmp/z
grep -e 'x' /tmp/z ; echo $PIPESTATUS
works as I expect, returning 1 if the pattern is 'x' (as shown), and 0 if the pattern is 'z'.
Why?
PIPESTATUS is actually a BASH array variable containing a list of exit status values from the processes in the most-recently-executed foreground pipeline.
To print all the exit statuses, you need to use it as:
echo "z" | grep -e 'x' ; echo ${PIPESTATUS[@]}
0 1
Where 0 is exit status of first echo command and 1 is the exit status of grep command.
When you use echo $PIPESTATUS it just prints first element of array.
To check the grep command status you don't even need to use PIPESTATUS.
You should just use $?:
echo "z" | grep -q 'x' ; echo $?
1
