Script for shifting days for timestamp of commit in Git

git-rcd

#!/bin/bash
# commit 
# number of days before for shifting to

commit="$1"
daysago=$2
temp_branch="temp-rebasing-branch"
current_branch="$(git rev-parse --abbrev-ref HEAD)"

original_timestamp="$(git show -s --format=%ct "$commit")"  #unix timestamp here
ori_readable=$(date -d "@$original_timestamp")              #print this out if you need it
new_timestamp=$(( $original_timestamp - 86400 * $daysago))  #shift n days for original timestamp
date_timestamp=$(date -d "@$new_timestamp")                 #convert calculated timestamp to readable timestamp 
date_r=$(date -R -d "$date_timestamp")                      #convert timestamp to git compatible timestamp


if [[ -z "$commit" ]]; then
    exit 0
fi

git checkout -b "$temp_branch" "$commit"
GIT_COMMITTER_DATE="$date_timestamp" GIT_AUTHOR_DATE="$date_timestamp" git commit --amend --no-edit --date "$date_r"
git checkout "$current_branch"
git rebase --autostash --committer-date-is-author-date "$commit" --onto "$temp_branch"
git branch -d "$temp_branch"