How can one change the timestamp of an old commit

Question

The answers to How to modify existing, unpushed commits? describe a way to amend previous commit messages that haven't yet been pushed upstream. The new messages inherit the timestamps of the original commits. This seems logical, but is there a way to also re-set the times?

Answer 1

This changes the date (timestamp) for the last commit

git commit --amend --date "Thu May 28 18:21:46 2015 +0530"

Answer 2

Use git filter-branch with an env filter that sets GIT_AUTHOR_DATE and GIT_COMMITTER_DATE for the specific hash of the commit you're looking to fix.

This will invalidate that and all future hashes.

Example:

If you wanted to change the dates of commit 119f9ecf58069b265ab22f1f97d2b648faf932e0, you could do so with something like this:

git filter-branch --env-filter \
    'if [ $GIT_COMMIT = 119f9ecf58069b265ab22f1f97d2b648faf932e0 ]
     then
         export GIT_AUTHOR_DATE="Fri Jan 2 21:38:53 2009 -0800"
         export GIT_COMMITTER_DATE="Sat May 19 01:01:01 2007 -0700"
     fi'

Answer 3

Just do git commit --amend --reset-author --no-edit. For older commits, you can do an interactive rebase and choose edit for the commit whose date you want to modify.

git rebase -i <ref>

Then amend the commit with --reset-author and --no-edit to change the author date to the current date:

git commit --amend --reset-author --no-edit

Finally continue with your interactive rebase:

git rebase --continue

Answer 4

Building on theosp's answer, I wrote a script called git-cdc (for change date commit) that I put in my PATH.

The name is important: git-xxx anywhere in your PATH allows you to type:

git xxx
# here
git cdc ... 

That script is in bash, even on Windows (since Git will be calling it from its msys environment)

#!/bin/bash
# commit
# date YYYY-mm-dd HH:MM:SS

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

date_timestamp=$(date -d "$datecal" +%s)
date_r=$(date -R -d "$datecal")

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"

With that, you can type:

git cdc @~ "2014-07-04 20:32:45"

That would reset author/commit date of the commit before HEAD (@~) to the specified date.

git cdc @~ "2 days ago"

That would reset author/commit date of the commit before HEAD (@~) to the same hour, but 2 days ago.

---

Ilya Semenov mentions in the comments:

For OS X you may also install GNU coreutils (brew install coreutils), add it to PATH (PATH="/usr/local/opt/coreutils/libexec/gnubin:$PATH") and then use "2 days ago" syntax.

Answer 5

You can do an interactive rebase and choose edit for the commit whose date you would like to alter. When the rebase process stops for amending the commit you type in for instance:

git commit --amend --date="Wed Feb 16 14:00 2011 +0100"

Afterwards you continue your interactive rebase.

UPDATE (in response to the comment of studgeek): to change the commit date instead of the author date:

GIT_COMMITTER_DATE="Wed Feb 16 14:00 2011 +0100" git commit --amend

The lines above set an environment variable GIT_COMMITTER_DATE which is used in amend commit.

Everything is tested in Git Bash.

Answer 6

The following bash function will change the time of any commit on the current branch.

Be careful not to use if you already pushed the commit or if you use the commit in another branch.

# rewrite_commit_date(commit, date_timestamp)
#
# !! Commit has to be on the current branch, and only on the current branch !!
# 
# Usage example:
#
# 1. Set commit 0c935403 date to now:
#
#   rewrite_commit_date 0c935403
#
# 2. Set commit 0c935403 date to 1402221655:
#
#   rewrite_commit_date 0c935403 1402221655
#
rewrite_commit_date () {
    local commit="$1" date_timestamp="$2"
    local date temp_branch="temp-rebasing-branch"
    local current_branch="$(git rev-parse --abbrev-ref HEAD)"

    if [[ -z "$date_timestamp" ]]; then
        date="$(date -R)"
    else
        date="$(date -R --date "@$date_timestamp")"
    fi

    git checkout -b "$temp_branch" "$commit"
    GIT_COMMITTER_DATE="$date" git commit --amend --date "$date"
    git checkout "$current_branch"
    git rebase "$commit" --onto "$temp_branch"
    git branch -d "$temp_branch"
}