Linux Basic — Automation-Ready Scripts

Automation-Ready Scripts

Scripts designed for cron or systemd must run correctly without a human watching. That means no terminal, no $PATH assumptions, no interactive prompts.

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The Checklist

Requirement	Implementation
Non-interactive	No read, no prompts, no select
Absolute paths	#!/usr/bin/env bash or /bin/bash, full paths to commands
Explicit $PATH	Set PATH=/usr/local/bin:/usr/bin:/bin at top
Set strict mode	set -euo pipefail + trap for cleanup
Log everything	Redirect to a log file or use logger
Exit codes matter	Return 0 on success, nonzero on failure
Alert on failure	Email, Slack, PagerDuty when exit != 0
Idempotent	Running twice doesn’t break things
Lock file	Prevent concurrent runs with flock

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Template

#!/usr/bin/env bash
set -euo pipefail

# explicit PATH
PATH=/usr/local/bin:/usr/bin:/bin
export PATH

LOGFILE="/var/log/myautomation.log"
LOCKFILE="/var/run/myautomation.lock"

log() { echo "$(date '+%F %T') $*" | tee -a "$LOGFILE"; }
die() { log "ERROR: $*"; exit 1; }

# prevent concurrent runs
exec 9>"$LOCKFILE"
flock -n 9 || die "already running"

trap 'rm -f "$LOCKFILE"' EXIT

log "starting"
# do work here
log "complete"

Use logger -t myautomation to send messages to syslog if you prefer centralized logs.

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Idempotency

An idempotent script can run multiple times safely:

• Check if the target already exists before creating it
• Use rsync with --update instead of blindly copying
• mkdir -p instead of mkdir

[[ -d /backup/latest ]] || mkdir -p /backup/latest
rsync -a --delete /data/ /backup/latest/

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Alerting on Failure

Cron emails output by default (if mail is configured). For modern alerting:

# at end of script
if [[ $? -ne 0 ]]; then
    curl -X POST https://hooks.slack.com/... -d '{"text":"backup failed"}'
fi

Or wrap the cron job:

0 2 * * * /opt/backup.sh || echo "backup failed" | mail -s "ALERT" ops@example.com

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Next → Automated Backup Script