Crontab Line Parser

Author: Daniel Siechniewicz daniel@nulldowntime.com

Intro

This is a command line application that parses a single line in crontab format and returns a table with all time definitions expanded to their numeric equivalents, plus a command "as is".

The implementation deliberately doesn't use existing cron modules.

Setting up

No external (non-standard) packages are used. As long as go is installed it should be possible to compile and/or run this utility. go.mod is provided to be able to use this outside of go path.

Run in DEV

go run parse_cron.go "*/15 0 1,15 * 1-5 /usr/bin/find"

Build

go build -o parse_cron

Run binary

./parse_cron "*/15 0 1,15 * 1-5 /usr/bin/find"

Tests

For now only the parseCronLine is tested with valid an invalid input lines. Please see parse_cron_test.go for details.

Run tests

go test

Caveats/Missing features

Comments are not handled
The command is not sanitized/escaped at the moment
No effort is made to fix any data, it's either handled as is, or it's a failure
Similarly, nothing is sorted, duplicate list items are not removed, etc
There are certainly more cases to be handled, these are just the preliminary ones (i.e. should a too large interval be ignored, as it is now, or an error?)
Some valid configurations are not supported, especially where there exists some ambiguity in the crontab format, like day of the week number 0
Special strings (@yearly, etc) are not supported

nulldowntime / cron_parser