Error Detection
Detect errors early during execution.
Shell Script · Lesson
Shell Scripting · Lesson 18
Debugging & Traps in Shell Scripting
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components/shell/ShellLessons.jsWhat is Debugging?
Debugging is the process of finding and fixing errors in a script. Shell provides built-in tools to help trace execution and handle failures.
Why Debugging is Important?
Stability
Prevent scripts from crashing silently.
Reliability
Improve script reliability and safety.
Debugging Tools in Shell
set -x– Print commands before executionset -e– Exit on errorset -u– Treat unset variables as errorstrap– Catch signals and cleanup
Debugging Examples
1. Debug Mode with set -x
Prints each command before executing it.
terminal — bash
debug#!/bin/bash
set -x
name="Linux"
echo "Hello $name"
2. Exit on Error (set -e)
Stops script execution when a command fails.
terminal — bash
debug#!/bin/bash
set -e
mkdir testdir
cd testdir2 # This will fail
echo "This line will not run"
3. Unset Variable Check (set -u)
Treats unset variables as errors.
terminal — bash
debug#!/bin/bash
set -u
echo $UNDEFINED_VAR
4. Trap Signals
Execute commands when script exits or receives signals.
terminal — bash
debug#!/bin/bash
trap "echo 'Script interrupted'; exit" SIGINT
while true
do
echo "Running..."
sleep 2
done
Best Practices
Debugging Tips
- Use set -e in production scripts.
- Use trap to clean up temporary files.
- Test scripts with invalid inputs.
- Remove debug output before production.
Practice Task – Debugging
- Create a script that exits on error.
- Use trap to catch Ctrl+C.
- Enable debug mode and observe output.
Next lesson: Logging & Redirection