Add Checkout Old Version Of A File as a git til.

README.md

@@ -13,6 +13,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 
 ### git
 
+- [Checkout Old Version Of A File](git/checkout-old-version-of-a-file.md)
 - [Checkout Previous Branch](git/checkout-previous-branch.md)
 - [Delete All Untracked Files](git/delete-all-untracked-files.md)
 - [Dry Runs in Git](git/dry-runs-in-git.md)

git/checkout-old-version-of-a-file.md

@@ -0,0 +1,13 @@
+# Checkout Old Version Of A File
+
+When you want to return to a past version of a file, you can reset to a past
+commit. When you don't want to abandon a bunch of other changes, this isn't
+going to cut it. Another option is to just checkout the particular file as
+it was at the time of a past commit.
+
+If the sha of that past commit is `72f2675` and the file's name is
+`some_file.rb`, then just use checkout like so:
+
+```
+$ git checkout 72f2675 some_file.rb
+```