Cron Expression Parser

This is a CLI to parse and display on a easy-to-understand table the times that the command will run, and the command itself. Also display the next 5 expected instances of the cron.

cronParser */15 0 1,15 * 1-5 /usr/bin/find

Produces:

minute        0 15 30 45
hour          0
day of month  1 15
month         1 2 3 4 5 6 7 8 9 10 11 12
day of week   1 2 3 4 5
command       /usr/bin/find

Friday, 1 November 2024, 00:00:00 Greenwich Mean Time
Friday, 1 November 2024, 00:15:00 Greenwich Mean Time
Friday, 1 November 2024, 00:30:00 Greenwich Mean Time
Friday, 1 November 2024, 00:45:00 Greenwich Mean Time
Friday, 15 November 2024, 00:00:00 Greenwich Mean Time

Details Of Implementation

This Parser implementation follows the LEXER => TOKEN => PARSER => CRON JOB EXPRESSION approach.

The code is organised feature based, so there is a package lexer and a package parser, Main connects both of them to produce the application result.

How To Run

Requirements

This is a Scala project, built using sbt, so ideally we will require the sbt to be installed. It can easily be installed using sdkman or homebrew, more details in https://www.scala-sbt.org/1.x/docs/Installing-sbt-on-Mac.html

#SDKMAN!
sdk install java $(sdk list java | grep -o "\b8\.[0-9]*\.[0-9]*\-tem" | head -1)
sdk install sbt

# Homebrew
brew install sbt

Running The Tests

Once SBT is installed, to run the tests suite, simply use sbt from the root directory of the project.

sbt test

The command will build and run the tests

Running the App with SBT

An option to run the application can be using directly sbt, for that we will need to scape the string argument.

sbt "run \"*/15 0 1,15 * 1-5 /usr/bin/find\""

Building the JAR to run from the CLI

For the building of the fatJar, we are using sbt-assembly, so run the command and this will build a jar for later execution:

sbt assembly

Once this has run, you should see the jar in the following path: ${projectDir}/target/scala-2.13/CronParser-assembly-0.1.0-SNAPSHOT.jar

With that jar we can then manually test the parser:

java -jar target/scala-2.13/CronParser-assembly-0.1.0-SNAPSHOT.jar "*/15 0 1,15 * 1-5 /usr/bin/find"

Which produces:

minute        0 15 30 45
hour          0
day of month  1 15
month         1 2 3 4 5 6 7 8 9 10 11 12
day of week   1 2 3 4 5
command       /usr/bin/find

Friday, 1 November 2024, 00:00:00 Greenwich Mean Time
Friday, 1 November 2024, 00:15:00 Greenwich Mean Time
Friday, 1 November 2024, 00:30:00 Greenwich Mean Time
Friday, 1 November 2024, 00:45:00 Greenwich Mean Time
Friday, 15 November 2024, 00:00:00 Greenwich Mean Time