cronjob: idempotent CRUD over a user crontab

[ralyodio]

cronjob installs, lists and removes scheduled jobs without ever installing one twice.

A crontab has no identity: nothing in the file says which line is the nightly summary. So the obvious way to install a job is to append, and the obvious consequence is the job once per deploy.

Identity comes from a marker comment — a managed job is exactly two lines:

# cli-tools:cronjob nightly-summary
0 9 * * * /usr/bin/whatever

• set replaces in place, so run 1 and run 1000 leave a byte-identical file and a clean diff.
• remove on an absent id changes nothing and exits 0.
• Duplicate ids from a hand edit collapse onto the first — leaving them means the job still fires twice after a "fix".
• Everything outside a marker block is preserved exactly: hand-written entries, MAILTO, PATH, comments.

Three silent failures it handles

Trap	Why it bites
% in a command	cron reads the first unescaped one as end-of-command and feeds the rest in as stdin, so date +%Y-%m-%d runs as date + and quietly does the wrong thing
No trailing newline	some crons ignore the last line — a job that looks installed and never runs
crontab - replaces the whole file	read-modify-write over shared state; the write holds an flock so two deploys landing together cannot drop each other's job

Verification

21 unit tests, plus an end-to-end run against a real crontab carrying 17 unmanaged lines: three set runs produced byte-identical output with one copy of the job and % escaped to \%, two remove runs were idempotent, and the file came back identical to the pre-test backup. tsc --noEmit clean.

Usage

cronjob list                   [--host dev2]
cronjob set <id> --schedule '0 9 * * *' --command '...' [--host dev2] [-n]
cronjob remove <id>            [--host dev2]

First use is the coinpayportal nightly summary, which has never had a caller — no Railway service in the project has a cronSchedule (checked all 72) and dev2 has no host cron or systemd timer for it.

🤖 Generated with Claude Code

[github-actions]

ThreatCrush Security Scan

23 finding(s)

HIGH/CRITICAL: 4 | MEDIUM: 10 | LOW: 9

Severity	Rule	Location
HIGH	sh-remote-script-execution	root-ubuntu.sh:3227
HIGH	sh-remote-script-execution	root-ubuntu.sh:3228
HIGH	sh-remote-script-execution	root-ubuntu.sh:4840
HIGH	sh-remote-script-execution	root-ubuntu.sh:4844
MEDIUM	sh-remote-script-execution	root-ubuntu.sh:4993
MEDIUM	redos-nested-quantifier	src/domain-free.ts:56
MEDIUM	redos-nested-quantifier	src/emoji.ts:167
MEDIUM	redos-nested-quantifier	src/icon.ts:166
MEDIUM	redos-nested-quantifier	src/mail.ts:1042
MEDIUM	sql-template-interpolation	src/users-dump.ts:487
MEDIUM	sql-string-concatenation	src/users-dump.ts:507
MEDIUM	sql-template-interpolation	src/users-dump.ts:540
MEDIUM	sql-string-concatenation	src/users-dump.ts:574
MEDIUM	redos-nested-quantifier	src/wcag.ts:556
LOW	secret-generic-credential	src/credentials.ts:36
LOW	secret-generic-credential	src/user-export.ts:632
LOW	secret-generic-credential	src/user-export.ts:638
LOW	secret-generic-api-key	test/credentials.test.ts:208
LOW	secret-generic-credential	test/mail.test.ts:141
LOW	secret-generic-credential	test/shorten.test.ts:36
LOW	secret-database-url	test/users-dump.test.ts:108
LOW	secret-database-url	test/users-dump.test.ts:119
LOW	secret-database-url	test/users-dump.test.ts:120

Snippets are redacted; ThreatCrush never prints matched credential material.