Custom Python/Shell Script for pre-commit

2 min readJun 2, 2022

Motivation

In this post, I would show how to use custom Python and Shell scripts used in pre-commit. pre-commit is a framework for managing and maintaining multi-language pre-commit hooks.

I regularly use pre-commit hooks like trimming trailing-white or end-of-file-fixer etc. Besides those, this time I try to run a custom Python script which checks for some rules.

(Note: For basic usage, please refer to https://pre-commit.com/ . )

Code

Python Script

Example custom.py file for the custom check.

import sysprint("Hello from custom.py")  # Stdout only printed when Failedtry:
    1 / 0
except Exception as e:
    sys.exit(e)

To tell that the script failed, return non-zero exit().
sys.exit(e) returns the message e “division by zero” and exit code:1.

Note that stdout “Hello from custom.py” is only shown when Failed.Add those lines to .pre-commit-config.yaml . With those settings, python will run the custom script.

- repo: local
  hooks:
    - id: custom-script-py
      name: custom-script-py
      entry: python custom.py
      language: python
      pass_filenames: false

To test the config, run:

pre-commit run --all-files

Output will be like:

custom-script-py..................................Failed
- hook id: custom-script-py
- exit code: 1Hello from custom.py
division by zero

Shell Script

Example of custom.sh file:

#!/bin/bashecho "Hello from custom.sh"expr 1 / 0

Add this to .pre-commit-config.yaml file.

- repo: local
  hooks:
    - id: custom-script-sh
      name: custom-script-sh
      entry: custom.sh
      language: script
      pass_filenames: false

Output will be like:

custom-script-sh..................................Failed
- hook id: custom-script-sh
- exit code: 2Hello from custom.sh
expr: division by zero

Summary

I have shown examples to run custom Python and Shell scripts with pre-commit.