Bash Scripting Masterclass: Automating the Boring Stuff

The shell is your home. Bash functions are your furniture. A good DevOps engineer automates everything that needs to be done more than twice.

The Shebang

Always start with #!/bin/bash. This tells the kernel which interpreter to use.

Strict Mode

Bash is forgiving, which is bad for automation. Add this to the top of every script:

set -euo pipefail

• -e: Exit immediately if a command fails (returns non-zero).
• -u: Treat unset variables as an error (prevents rm -rf /$UNDEFINED_VAR).
• -o pipefail: If a command in a pipe fails (cmd1 | cmd2), the whole thing fails.

Variables and Expansion

Always quote your variables.

FILE="My File.txt"
rm $FILE    # ERROR: Tries to remove "My" and "File.txt"
rm "$FILE"  # CORECT: Removes "My File.txt"

Loops: Iterating Files

Don't parse ls. Use globs.

for file in *.jpg; do
    echo "Processing $file..."
    convert "$file" "${file%.jpg}.png"
done

${file%.jpg} removes the extension. Bash string manipulation is surprisingly powerful.

Functions

Modularity makes scripts readable.

log() {
    local level=$1
    shift
    echo "[$(date +'%Y-%m-%d %H:%M:%S')] [$level] $*"
}

log "INFO" "Backup started"

Trap: Cleaning Up

What if the user hits Ctrl+C? Use trap to run cleanup code.

temp_file=$(mktemp)
trap "rm -f $temp_file" EXIT

echo "Working..." > "$temp_file"
# Even if script errors or exits here, file is deleted.

Bash isn't just for glue code. With discipline, it's a powerful programming language.