Randomly rejects commits. https://twitter.com/mfeathers/status/963587422507421698

random-reject-pre-commit.sh

#!/bin/bash

# Make this executable and name it .git/hooks/pre-commit to have commits
# randomly rejected with a prompt to rethink it. The odds are higher for
# longer commits

set -eu

# How many lines a commit must have before it's considered long and should
# have the highest odds of getting an extra prompt
LONG_COMMIT_THRESHOLD=150

# The percentage of long commits that will be prompted
LONG_COMMIT_PROMPT_ODDS=50

# The percentage of short commits that will be prompted
SHORT_COMMIT_PROMPT_ODDS=10


rough_line_count=$(
    git diff --cached \
        | grep -E '^[+-]' \
        | wc -l
)
if [ $rough_line_count -gt $LONG_COMMIT_THRESHOLD ]; then
    rough_line_count=$LONG_COMMIT_THRESHOLD
fi

# $RANDOM is in the range 0 - 32768, thus assuming odds of 50%/10% and long commit
# threshold of 150 we want to scale the line count so that [0, 150] -> [3276, 16384]
high_threshold="$(( 32768*$LONG_COMMIT_PROMPT_ODDS/100 ))"
low_threshold="$(( 32768*$SHORT_COMMIT_PROMPT_ODDS/100 ))"
scale_factor="$(( ($high_threshold - $low_threshold)/$LONG_COMMIT_THRESHOLD ))"
datum="$(( $rough_line_count*$scale_factor + $low_threshold ))"
if [ $RANDOM -lt $datum ]; then
    echo >&2 'Please think a bit more about this.'
    exit 1
fi