Git grep in all merges/commits into the current branch since a specific date

git-grep-over-time.sh

#!/usr/bin/env bash
if [ $# -eq 0 ]
then
    self=$(basename $0)
    echo "Usage: $self pattern directory"
    exit 1
fi

pattern=$1
since="--since=2015-12-01"

for revision in `git --no-pager log $since --first-parent --grep="Merge pull request" --format="%H"`
do
    timestamp=`git --no-pager log --format='%at' -n 1 $revision`
    count=`git --no-pager grep --extended-regexp $pattern $revision | wc -l | tr -d '[[:space:]]'`
    echo $revision,$timestamp,$count
done