Repotracer: compute stats command over the last commit of every day in a repo

tracer.sh

#!/bin/bash

set -eou pipefail
# A script that runs a command on every day of the last year over the commmit
# history of a git repository. The command is passed as the first argument to
# the script. The script will run the command in the directory of the commit
# that is being processed. The script will also pass the date of the commit as
# the second argument to the command.

function usage {
    echo "Usage: $0 <command>"
    echo "Runs a command on every day of the last year over the commit history"
    echo "of a git repository. The command is passed as the first argument to"
    echo "the script. The script will run the command in the directory of the"
    echo "commit that is being processed. The script will also pass the date of"
    echo "the commit as the second argument to the command."
}   

if [ $# -ne 1 ]; then
    usage
    exit 1
fi

outfile=`pwd`/output.txt
echo $outfile


##Either use the date command or gdate command depending on the OS
if date -v -1d > /dev/null 2>&1; then
    dateDelta() { date -v -"$1d" +%F; }
else
    dateDelta() { date --date="$1 day ago"; }
fi

cmd=$1

oldcommit=""
commit=""

runCommandOnDate() {
    date=$1
    # Get the commit hash for the day
    oldcommit=$commit
    commit=$(git rev-list -n 1 --before="$date" master)

    # if the commit is the same as the previous day, reuse the output
    if [ "$commit" == "$oldcommit" ]; then
        output=$(echo $raw_output | jq -c --arg date $date '{date: $date} + .')
        continue
    fi

    # Checkout the commit, redirecting stderr to /dev/null to avoid printing
    git checkout $commit > /dev/null 2>&1
    raw_output=$(eval $cmd)

    output=$(echo $raw_output | jq -c --arg date $date '{date: $date} + .')
}

for i in {365..0}
do
    echo -ne "$i days remaining\r"

    runCommandOnDate $(dateDelta $i)
    echo $output >> "$outfile"
done