Overview

At Wolf Software we write a lot of bash scripts for many purposes and the one thing that we found lacking was a simple to use debugging tool.

Trapper is something that weas developed originally for internal use to debug scripts we release with the aim being a simple plugin that required minimal changes to the original script.

Trapper is capable of capturing a large array of runtime errors and attempts to point to where the error happened.

Usage

Simply source trapper at the top of your script and then execute it as normal.

Trapper works by setting a trap for any errors and attempts to display where the errors happened.

Truncated snippet

set -Eeuo pipefail

function trap_with_arg()
{
    func="$1";
    shift

    for sig ; do
        # shellcheck disable=SC2064
        trap "$func $sig" "$sig"
    done
}

trap_with_arg 'failure ${?}' ERR EXIT

It is capable of detecting errors in a many different scenarios.

Scenario	Requirements	Results
Single script	Include trapper.sh	Reports filename, line number and code snippet.
Executing scripts	Include trapper.sh (in all scripts)	Reports filename, line number and code snippet for full stack trace (calling scripts).
Including scripts	Include trapper.sh (only in parent script)	Reports filename, line number and code snippet of the failing included script.

Examples

Testing for unset (unbound) variables

Single script attempt to use an unbound variable.

Source

Testing execute stack (scripts calling scripts)

Parent script executing child script with error in the final child.

Source

Testing source stack (scripts including scripts)

Parent script including (sourcing) child scripts with an error in the final child.

Source