Exit codes ($?) in Bash Scripting

Introduction

Exit codes tell us if a command worked or failed. They help scripts decide what to do next.

Check if a file was copied successfully before moving on.

Verify if a program ran without errors before starting another task.

Detect if a command failed and show a friendly message to the user.

Stop a script early if a critical step did not complete correctly.

Syntax

Bash Scripting

echo $?  # shows the exit code of the last command

Exit code 0 means success; any other number means an error.

Always check $? right after the command you want to test.

Examples

Lists files in /tmp and then prints the exit code. 0 means success.

Bash Scripting

ls /tmp
 echo $?

Tries to list a non-existing folder, then prints exit code. Non-zero means error.

Bash Scripting

ls /not_exist
 echo $?

Creates a folder and prints exit code to confirm success.

Bash Scripting

mkdir newfolder
 echo $?

Sample Program

This script creates a folder and checks if it worked using exit codes. Then it removes the folder and checks again.

Bash Scripting

#!/bin/bash

mkdir testfolder
if [ $? -eq 0 ]; then
  echo "Folder created successfully."
else
  echo "Failed to create folder."
fi

rm -r testfolder
if [ $? -eq 0 ]; then
  echo "Folder removed successfully."
else
  echo "Failed to remove folder."
fi

Important Notes

Always check the exit code immediately after the command you want to verify.

Use exit codes in scripts to handle errors gracefully and avoid surprises.

Common exit codes: 0 = success, 1 = general error, other numbers can mean specific errors.

Summary

Exit codes tell if a command worked or failed.

0 means success; other numbers mean errors.

Check $? right after a command to get its exit code.