How good is a commit? The bigger the commit message, more thought was put into that commit

git-bacon_ratio.sh

#!/bin/sh

CSV_OUTPUT=0

_main()
{
	header_printed=""
	for commit in $(repository_commits)
	do 
		changed_lines=$(diff_stat_of $commit)
		lines_explaining=$(lines_from_commit $commit)
		ratio=$(ratio_between $lines_explaining $changed_lines)

		if [ "$CSV_OUTPUT" == "1" ]
		then
			if [ "$header_printed" != "yes" ]
			then
				echo "commit,ratio,commit lines,changes"
				header_printed="yes"
			fi
			echo "${commit},${ratio},${lines_explaining},${changed_lines}"
		else
			echo "$commit ratio of explanation is $ratio% ($lines_explaining lines / $changed_lines changes)"
		fi
	done
}

repository_commits()
{
	if [ ! -d "${PWD}/.git" ]
	then
		_error "Not inside a Git repository. Type $0 -h"
	fi

	git log --oneline | awk '{print $1}'
}

diff_stat_of()
{
	commit=$(echo_when_not_empty $@)
	diff=$(git diff --stat $commit^ 2> /dev/null)
	if [ $? -ne 0 ]
	then
		echo 1 # first commit has no diff
	fi
    
	echo $diff | tail -n1 | awk -F , '{print $2}' | sed 's/[^0-9]//g'
}

lines_from_commit()
{
	commit=$(echo_when_not_empty $@)

	git show --format="%s%n%n%b" --no-patch $commit | wc -l | sed 's/ //g'
}

# Usage: ratio_between <commit message lines> <commit additions>
ratio_between()
{
	message_lines=$1
	diff_additions=$2
	# http://stackoverflow.com/a/20562313/447920
	bc_program=$(cat <<-EOT
		define trunc(x) { auto s; s=scale; scale=0; x=x/1; scale=s; return x };
		scale=2;
		b=(${message_lines}/${diff_additions})*100;
		print trunc(b);
	EOT
	)

	echo $bc_program | bc
}

# Usage: _error "Some warning"
_error () { echo "Error: $@" 1>&2; exit 2; }
# Usage: assert_not_empty <subject> [error message]
echo_when_not_empty() { test -z "$1" && _error "${error_msg:-'Argument is empty.'}" || echo $1; }

while getopts ":hvc" option
do
	case $option in
		v)
			echo "$0 version 1.0.0"
			exit 0
			;;
		c)
			CSV_OUTPUT=1
			;;
		h)
			cat <<-EOT
				Usage: $0 [options]

				Prints the ratio between the lines in commit messages and changes
				made in the source code.

				Options:
				    -v      Displays version information.
				    -h      This friendly help message.
				    -c      Machine friendly output, CSV style.

				Send bugs or suggestions to Augusto Pascutti <augusto.hp@gmail.com>
			EOT
			exit 0;
	esac
done

_main
	
#vim: ft=shell noet ts=4 sw=4: