Bash

❗ Error Handling in Bash

Robust error handling ensures your Bash scripts behave predictably when something goes wrong. This is especially important in automation, backups, and server management scripts.

📌 Why Error Handling Matters

Without error handling:

🛑 Exit Codes ($?)

Every Bash command returns an exit code:

ls /nonexistent
echo $?   # 2 → Error

Use exit codes in conditions:

if [ $? -ne 0 ]; then
  echo "Command failed"
fi

⚙️ set Options for Strict Error Checking

set -e

set -e
cp file.txt /protected/path/    # If fails, script stops

set -u

set -u
echo $username   # Error if 'username' not set

set -o pipefail

set -o pipefail
grep "something" file.txt | sort | head

Without pipefail, only the last command’s exit code is checked.

🧲 trap – Catch and Handle Errors or Signals

You can trap signals like EXIT, ERR, INT:

trap 'echo "An error occurred."' ERR

Cleanup Example:

#!/bin/bash
set -e

cleanup() {
  echo "Cleaning up temporary files..."
  rm -f /tmp/tempfile
}
trap cleanup EXIT

touch /tmp/tempfile
cp /nonexistent /tmp/tempfile   # Will trigger trap

📋 Check Command Before Use

Use command -v to verify a tool exists before using it:

if ! command -v rsync &> /dev/null; then
  echo "rsync not found. Please install it." >&2
  exit 1
fi

🔁 Wrapping Commands with ||

Use || to run fallback logic:

mkdir /protected/dir || { echo "Failed to create dir"; exit 1; }

✅ Best Practices

Tip Reason
Use set -euo pipefail Makes script safer
Use trap Ensure cleanup
Check exit codes Prevent silent failures
Redirect stderr command 2>error.log
Quote your variables Avoid word splitting

🧪 Example Script

#!/bin/bash
set -euo pipefail
trap 'echo "Something went wrong"; exit 1' ERR

backup_file="/tmp/backup.tar.gz"

echo "Starting backup..."
tar -czf "$backup_file" /important/data
echo "Backup completed at $backup_file"

📚 Related Topics

📁 File: advance/error-handling.md
Author: Kashif Alam

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