Error Detection
Detect if a command ran successfully.
Shell Script · Exit Status
Shell Scripting · Lesson 17
Exit Status
Understand exit status in Linux commands. Use $? in scripts. Error handling technique. Build reliable automation scripts.
What is Exit Status?
Every command executed in Linux returns an exit status. It is a numeric value that tells whether a command succeeded or failed.
By convention:
- 0 → Success
- Non-zero → Failure
Why Exit Status Matters
Flow Control
Control script execution based on success or failure.
Debugging
Helps identify which command failed.
How to Check Exit Status
check exit status
exit-statuscommand
echo $?
Exit Status Examples
1. Basic Exit Status
Every command returns an exit status after execution.
terminal — bash
exit-statusls /home
echo $?
2. Success vs Failure
0 means success, non-zero means failure.
terminal — bash
exit-statusls /home
echo "Exit status: $?"
ls /notexist
echo "Exit status: $?"
3. Using Exit Status in Condition
Use $? to check if a command succeeded.
terminal — bash
exit-statusmkdir testdir
if [ $? -eq 0 ]; then
echo "Directory created successfully"
else
echo "Failed to create directory"
fi
4. Custom Exit Codes
Use exit to define your own exit status.
terminal — bash
exit-statusif [ -f "/etc/passwd" ]; then
echo "File exists"
exit 0
else
echo "File not found"
exit 1
fi
Best Practices
Recommended Practices
- Always check exit status for critical commands.
- Use meaningful exit codes (0–255).
- Avoid ignoring failures silently.
- Use exit in scripts to stop execution when needed.
Practice Task – Exit Status
- Write a script that checks if a file exists.
- Exit with status 0 if found, 1 otherwise.
- Print meaningful messages.
Next lesson: Debugging & Traps