Cron Expression Parser

Introduction

This Python project provides a simple tool for parsing cron expressions. It interprets the individual fields of a cron expression (minute, hour, day of the month, month, day of the week) and the command to be executed. The tool then displays the times at which a given cron job will run.

Installation

Requirements

• Python 3.6 or higher

Setup

Clone this repository to your local machine using:

git clone https://github.com/atul107/cron-parser.git
cd cron-parser

Usage

To use the cron expression parser, run the main.py script from the command line, passing the cron expression as a single argument:

python main.py "*/15 0 1,15 * 1-5 /usr/bin/find"

This will output the parsed cron fields and the command, like so:

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

Ensure your cron string is enclosed in quotes to be correctly interpreted by the shell.

Development

Project Structure

The project contains three main files:

• cron_field.py: Defines the CronField class for parsing and displaying individual cron fields.
• cron_parser.py: Contains the CronParser class for parsing entire cron expressions using CronField instances.
• main.py: The entry point of the program, handling command-line input and displaying parsed results.

Running Tests

The test covers basic functionalities of both the CronField and CronParser classes:

• For CronField, it tests parsing of all field types: for every possible value, a range like 5-9, a list like 1,15,20, and a step value like /2.
• For CronParser, it includes tests for a valid cron string to check if the parsing is correctly applied, and also for an invalid cron string to ensure it raises a ValueError as expected.

Run the tests with the following command in your terminal:

python -m unittest tests/test_cron_parser.py

This command will discover and run all the tests defined in test_cron_parser.py, reporting the results in the terminal.