Add Find The Date That A File Was Added To The Repo as a git til

Author: jbranchaud

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_744 TILs and counting..._
+_745 TILs and counting..._
 
 ---
 
@@ -175,6 +175,7 @@ _744 TILs and counting..._
 - [Dropping Commits With Git Rebase](git/dropping-commits-with-git-rebase.md)
 - [Dry Runs in Git](git/dry-runs-in-git.md)
 - [Excluding Files Locally](git/excluding-files-locally.md)
+- [Find The Date That A File Was Added To The Repo](git/find-the-date-that-a-file-was-added-to-the-repo.md)
 - [Find The Initial Commit](git/find-the-initial-commit.md)
 - [Get The Short Version Of The Latest Commit](git/get-the-short-version-of-the-latest-commit.md)
 - [Grab A Single File From A Stash](git/grab-a-single-file-from-a-stash.md)

git/find-the-date-that-a-file-was-added-to-the-repo.md

@@ -0,0 +1,35 @@
+# Find The Date That A File Was Added To The Repo
+
+The `git log` command has a bunch of flags that you can use to filter
+commits and format their output.
+
+We can get `git log` to only show the date for a commit in the `short`
+format with the following flags:
+
+```bash
+$ git log --pretty=format:"%ad" --date=short
+```
+
+We can also get `git log` to filter commits to just those that have files
+being added:
+
+```bash
+$ git log --diff-filter=A
+```
+
+Like many `git` commands, we can restrict the output to those that match a
+path or file.
+
+```bash
+$ git log -- README.md
+```
+
+If we put all of these together, then we have a one-line command for getting
+the date a specific file was added to the repository:
+
+```bash
+$ git log --pretty=format:"%ad" --date=short --diff-filter=A -- README.md
+2015-02-06
+```
+
+See `man git-log` for more details.