Output when command exits with non-zero status

Question

For obvious reasons, entering the following on the command line results in non-zero status error.:
"echo AWK might do it | sed 's/it*$//' | grep it?"
How do I get Terminal to tell me the command that generated this error

Answer 1

The Terminal is not responsible for error messages, it is your shell. The default Mac OS X shell is bash
From the bash man page (man bash):
The return status of a pipeline is the exit status of the last command,
unless the pipefail option is enabled. If pipefail is enabled, the
pipeline's return status is the value of the last (rightmost) command
to exit with a non-zero status, or zero if all commands exit success-
fully.
But I must warn you that if you enable pipefail all the time, you might break existing scripts that do not expect that behavior.
Looking at your echo|sed|grep command line, there are no errors, not even grep. A non-zero exit status is not necessarily an error, as it is all in the eye of the beholder. From the grep man page:
Normally, exit status is 0 if selected lines are found and 1 otherwise.
But the exit status is 2 if an error occurred, unless the -q or --quiet
or --silent option is used and a selected line is found.
So in the case of grep an exit status of 2 means there was an error. A value of 0 or 1 means there was no error, but rather the difference between finding what you were looking for vs not finding.