How to display last command that failed when using bash set -e?

Question

I am using set -e to stop execution of a script on first error.

The problem is that this does not tell me what went wrong.

How can update a bash script so it will display me the last command that failed?

Answer 1

Instead of set -e, use an ERR trap; you can pass $BASH_LINENO in to get the specific line number on which the error occurred. I provide a script taking advantage of this in my answer at https://stackoverflow.com/a/185900/14122

To summarize:

error() {
   local sourcefile=$1
   local lineno=$2
   # ...logic for reporting an error at line $lineno
   #    of file $sourcefile goes here...
}
trap 'error "${BASH_SOURCE}" "${LINENO}"' ERR

Answer 2

1. make err.sh

   set -e
   trap 'echo "ERROR: $BASH_SOURCE:$LINENO $BASH_COMMAND" >&2' ERR
   

2. include it (. err.sh) in all your scripts.

3. replace any

   ... | while read X ; do ... ; done

   with

   while read X ; do ... ; done < <( ... )

   in your scripts for the trap to give the correct line number/command in the error message