Shell Scripting Patterns for DevOps

Shell scripts are everywhere in DevOps:

• setup scripts
• deployment hooks
• cron/systemd jobs
• CI steps
• quick maintenance tasks

Most production “script bugs” are caused by:

• missing error checks
• unquoted variables (whitespace/globbing bugs)
• silent failures in pipelines
• unclear logging

This tutorial shows hardened patterns you can copy.

Learning outcomes

You’ll learn:

• strict mode and safer Bash defaults
• how to structure scripts with functions
• how to handle arguments and usage
• safe cleanup and temporary files

1) Start with strict mode

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

What each option does:

• -e: exit on command failure
• -u: treat unset variables as errors
• pipefail: pipeline fails if any command fails

2) Add logging helpers

log()  { echo "[INFO]  $*" >&2; }
warn() { echo "[WARN]  $*" >&2; }
err()  { echo "[ERROR] $*" >&2; }

Use:

log "Starting backup"

3) Validate inputs early

Pattern:

• show usage
• exit non-zero on bad args

usage() {
  cat >&2 <<'EOF'
Usage:
  backup.sh <source_dir> <dest_dir>
EOF
}

if [[ $# -ne 2 ]]; then
  usage
  exit 2
fi

src="$1"
dst="$2"

4) Use functions to isolate steps

ensure_dir() {
  local dir="$1"
  mkdir -p "$dir"
}

copy_tree() {
  local src="$1" dst="$2"
  cp -a "$src" "$dst"
}

5) Safe file operations

Always quote variables:

cp -a "$src" "$dst"
rm -rf -- "$path"

-- prevents paths starting with - from being treated like flags.

6) Temporary files + cleanup

tmp="$(mktemp)"
cleanup() { rm -f "$tmp"; }
trap cleanup EXIT

# ... use $tmp

7) Example: copy with checks

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

log() { echo "[INFO] $*" >&2; }

usage() {
  cat >&2 <<'EOF'
Usage:
  copy-safe.sh <source> <destination>
EOF
}

if [[ $# -ne 2 ]]; then
  usage
  exit 2
fi

src="$1"
dst="$2"

if [[ ! -e "$src" ]]; then
  log "Source not found: $src"
  exit 1
fi

log "Copying $src -> $dst"
mkdir -p "$(dirname "$dst")"
cp -a "$src" "$dst"

log "Done"

Next steps

This completes your “Linux + automation” foundation. Next DevOps pages:

• Git & GitHub workflows
• GitHub Actions CI/CD
• Terraform (IaC) basics
• Ansible (idempotent configuration)
• Jenkins pipelines
• Monitoring & observability mindset