Add Using Commands With A Relative Date Format as a git til

git/using-commands-with-a-relative-date-format.md

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+# Using Commands With A Relative Date Format
+
+If you want to know what changed on a branch _since_ last week, you can more or
+less ask just like that:
+
+```bash
+$ git log --since="1 week ago"
+```
+
+Or, what has happened since yesterday:
+
+```bash
+$ git log --after="yesterday"
+```
+
+The `--since`/`--after` flags, and their counterparts `--until`/`--before`,
+accept a variety of date formats including _relative dates_.
+
+Relative dates can be used with other commands and even as a ref modifier. For
+instance, this is a way of comparing `develop` from a week ago with `develop`
+from two weeks ago:
+
+```bash
+$ git diff develop@{"1 week ago"} develop@{"2 weeks ago"}
+```
+
+[source](https://alexpeattie.com/blog/working-with-dates-in-git)