git-mtime is a Git extension that finds a last modified times through Git commits:

Git repositories provide records of deliberate updates through commit logs. By retrieving the last commit date for a specific file, we can find the last date a file was purposefully updated.

#!/bin/bash
path="${@: -1}"
dir=$(dirname "$path")

hash=$(git -C "$dir" log \
           --format="%ad %H" \
           --date=format:"%s" \
           --grep="\[date skip\]" \
           --invert-grep \
           -- $(basename "$path") |\
           sort -r |\
           awk '{ print $2 }' |\
           head -n1)

git -C "$dir" show --format="%ad" --quiet "${@:1:$#-1}" "${hash}"

Installation

Download git-mtime and symlink it to /usr/local/bin/git-mtime:

curl --remote-name --silent https://raw.githubusercontent.com/jeffkreeftmeijer/git-mtime/main/git-mtime
ln -s $(realpath git-mtime) /usr/local/bin/git-mtime

Usage

Execute git mtime with a path to a file in a Git repository:

git mtime file.txt

Mon Mar 6 18:24:11 2023 +0100

Even outside of the repository, git-mtime can find the commit history and find a file's last update date:

git mtime repository/file.txt

Mon Mar 6 18:24:11 2023 +0100

By relying on git-log internally, git-mtime supports Git's --date flag:

git mtime --date=format:"%F %R" repository/file.txt

2023-03-06 18:24

If a commit touches a file, but you don't want to modify the file's modified time, mark the commit with [date skip] in its commit message to make git-mtime ignore it:

echo "file.txt" >> repository/file.txt
git -C repository add . 
git -C repository commit --quiet --message 'Fix file.txt' --message "[date skip]" 
./git-mtime repository/file.txt

Mon Mar 6 18:24:11 2023 +0100