Error handling in bash

I’ve been learning about approaches to error handling in bash. I found Error handling in BASH, Exit Shell Script Based on Process Exit Code, Writing Robust Bash Shell Scripts and Bash: Error handling all of which contained a nugget of useful information.

Particularly I learned about $LINENO, set -e (equiv: set -o errexit), set -o pipefail, set -E, set -u (equiv: set -o nounset), set -C (equiv: set -o noclobber), #!/bin/bash -eEu, trap, shopt -s expand_aliases, alias, $PIPESTATUS, subshells, unset, and more.

If you call exit without specifying a return code then $? is used, I didn’t know that.

I found this code snippet that demos a relatively race-condition free method of acquiring a lock file:

if ( set -o noclobber; echo "$$" > "$lockfile") 2> /dev/null; 
   trap 'rm -f "$lockfile"; exit $?' INT TERM EXIT

   rm -f "$lockfile"
   trap - INT TERM EXIT
   echo "Failed to acquire lockfile: $lockfile." 
   echo "Held by $(cat $lockfile)"

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