A suggested pre-commit hook for projects with lots of legacy Python code

pre-commit hook

#!/bin/bash

set -euo pipefail

function lint_added_file () {
    # This is called for every file added in the current branch. This
    # is the place we should feel more free to validate files more
    # rigorously so that nothing we don't like can enter the codebase.

    # Get the type of the file and choose what to do.
    type=$(file --mime-type -b "$1")
    case $type in
        "text/x-shellscript")
            shellcheck "$1"
            ;;
        "text/x-python")
            isort -faas "$1"
            flake8 "$1"
            black -l 79 "$1"
            ;;
        *)
            echo "File $1 was not processed"
    esac
}

function lint_modified_file () {
    # This is called for every file modified in the current branch. We
    # can't be too rigorous here, as we risk failing validation for
    # regions that were not changed.

    # Get the type of the file and choose what to do.
    type=$(file --mime-type -b "$1")
    case $type in
        "text/x-shellscript")
            shellcheck "$1"
            ;;
        "text/x-python")
            flake8 "$1"
            ;;
        *)
            echo "File $1 was not processed"
    esac
}

# Iterate over the files added on this branch
for file in $(git diff --name-only --diff-filter=A develop)
do
    lint_added_file "$file"
done

# Iterate over the files modified on this commit
for file in $(git diff --name-only --diff-filter=M HEAD)
do
    lint_modified_file "$file"
done