Automation Scripts | Jungle Scripts

Automation scripts are where shell skills turn into real value. The goal isn’t “write code that works once” — it’s “write code that works repeatedly, safely, and is easy to operate”.

Design Principles (production‑ready)

•Idempotent: running twice shouldn’t break things
•Observable: logs to stderr/syslog + clear exit codes
•Safe defaults: fail fast (set -euo pipefail), quote variables, validate inputs
•Configurable: flags/env vars instead of hardcoding paths
•Locking: prevent overlapping runs (common with cron)

Backup Script Example

#!/bin/bash
set -e

BACKUP_DIR="/backup/$(date +%Y%m%d)"
SOURCE="/home/pranav"

mkdir -p "$BACKUP_DIR"
tar -czvf "$BACKUP_DIR/home.tar.gz" "$SOURCE"
echo "Backup completed: $BACKUP_DIR"

Improved pattern: safer mode + logging + validation

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

log() { echo "[INFO] $*" >&2; }
die() { echo "[ERROR] $*" >&2; exit 1; }

SOURCE="${1:-}"
[ -n "$SOURCE" ] || die "Usage: $0 /path/to/source"
[ -d "$SOURCE" ] || die "Source not found: $SOURCE"

BACKUP_ROOT="/backup"
BACKUP_DIR="$BACKUP_ROOT/$(date +%Y%m%d-%H%M%S)"
mkdir -p "$BACKUP_DIR"
log "Backing up $SOURCE to $BACKUP_DIR"
tar -czf "$BACKUP_DIR/archive.tar.gz" -C "$SOURCE" .
log "Done"

Log Rotation Script

#!/bin/bash
LOG_DIR="/var/log/myapp"
MAX_SIZE=10485760 # 10MB

for log in "$LOG_DIR"/*.log; do
size=$(stat -f%z "$log" 2>/dev/null || stat -c%s "$log")
if [ "$size" -gt "$MAX_SIZE" ]; then
mv "$log" "$log.$(date +%Y%m%d)"
gzip "$log.$(date +%Y%m%d)"
fi
done

Locking: prevent overlapping runs

If cron runs your script every 5 minutes but one run takes 8 minutes, you’ll get overlaps. Use a lock file or flock.

# Example using flock (preferred when available)
flock -n /var/lock/myjob.lock -c "/usr/local/bin/myjob.sh"

Scheduling + Observability

Automation should be “boring”: scheduled, logged, and alerting on failures.

•cron: simplest scheduler; redirect logs to a file
•systemd timers: better logs + dependencies + status

✅ Practice (30 minutes)

Write a script that rotates logs and adds a timestamp suffix, then compresses older logs.
Add argument validation and a --dry-run mode (print actions instead of executing).
Wrap it with flock so overlapping runs can’t happen.