Add Copy A File From Another Branch as a git til

git/copy-a-file-from-another-branch.md

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+# Copy A File From Another Branch
+
+After doing some work on a large feature branch, I wanted to split out some of
+the work into a separate smaller branch to create an initial PR. There were
+several files on the feature branch that I knew needed to be part of this
+smaller branch.
+
+To bootstrap this smaller branch, I need to check it out from main and then
+copy over the needed files.
+
+First, let's create a fresh branch:
+
+```bash
+$ git branch --show-current
+large-feature-branch
+
+$ git checkout main
+$ git checkout -b new-smaller-branch
+```
+
+Now I can start pulling over the files I care about:
+
+```bash
+$ git checkout large-feature-branch some/file/ICareAbout.js
+```
+
+This form of `git-checkout` looks on the specified branch for the specified
+file and copies that over to the index.
+
+Note: this will copy over any local, working tree changes that you've made to
+the named file.