elm-crontab

A crontab parser and humanizer in Elm -- for the basic UNIX syntax.

Inspired by rodinalex/elm-cron but rewritten from scratch using elm/parser and elm 0.19.1

Installation

elm install skovsboll/elm-cron

Run the examples using elm repl :

Parsing

import Cron exposing (fromString)

Cron.fromString " *   * *   *  *  "
-- (Ok (Cron Every Every Every Every Every))

Cron.fromString "* * */3 4 *"
-- Ok (Cron Every Every (Single (EveryStep 3)) (Single (Simple (Particle April))) Every)

Explaining

import Cron exposing (Atom(..), Cron(..), Expr(..), Term(..), Month(..))
import Humanizer

Humanizer.toString (Cron Every Every (Single (EveryStep 3)) (Single (Simple (Particle April))) Every)
-- "every minute, every hour, every third day of the month, in April, all week."

All together now

import Cron exposing (fromString)
import Humanizer
import Parser

case Cron.fromString "30 10 * * 3" of
    Ok cron ->
        Humanizer.toString cron
    Err deadEnds ->
        let
            _ = Debug.log "deadEnds" deadEnds
        in
            "error"
            

-- at 10:30, every day of the month, all year, on Wednesday.

Detecting syntax errors

Cron.fromString "1,2 * 30,31,32 * xyz"
--Err
--    [ { col = 15
--      , problem = Problem "Expected an integer from 1 through 31."
--      , row = 1
--      }
--    ]

Cron.fromString "* * * * xyz"
--Err 
--    [ { col = 12
--      , problem = Problem ("Expected the name of a week day (sun, mon, tue etc...) or a number from 0 through 6.")
--      , row = 1 }
--    , { col = 9
--      , problem = ExpectingSymbol "*"
--      , row = 1 }
--    ]

Where to go from here?

See the tests

Caveats

Only five segments supported. No fancy syntax supported.

Licence

BSD 0-Clause License (0BSD)

TLDR; Do what you want with it, but don't hold me liable for damages.

Contributing

Open issue Fork Fix Submit PR