feat(patches): 📝 Add some documentation and examples with patching.

85_patches/README.md

@@ -0,0 +1,144 @@
+# PATCHES
+
+Demonstrate different ways of creating patches.  
+
+REF: [36_git/sections/PATCHING.md](../36_git/sections/PATCHING.md)
+REF: [68_difftools/README.md](../68_difftools/README.md)
+
+NOTES:
+
+* Pure patches need to be applied at the same stage of code - otherwise the tooling errors in lots of places.  
+
+## Contents
+
+- [PATCHES](#patches)
+  - [Contents](#contents)
+  - [Tools](#tools)
+  - [Creation](#creation)
+    - [Git Staged](#git-staged)
+    - [Git Stashes](#git-stashes)
+    - [Diff](#diff)
+  - [Applying](#applying)
+    - [Git](#git)
+    - [Patch](#patch)
+  - [Scenarios](#scenarios)
+    - [Scenario 1](#scenario-1)
+    - [Scenario 2](#scenario-2)
+  - [Resources](#resources)
+
+TODO:
+
+* I want to be able create patch files of unstaged files.
+    * New files and modifications of files 
+* listing files in a patch  
+* Is it better to just zip up the changed files and decompress them over a directory?
+* multibyte characterset documents
+* git diff
+* git format-patch
+* baseless patches
+* Create a file with entire contents
+* Context and Unified Formats
+* Worktree diffs?
+
+## Tools
+
+| Tool | Description |
+| --- | --- |
+| diff | compare files line by line |
+| cmd | compare two files byte by byte |
+| diff3 | compare three files line by line |
+| git diff | Show changes between commits, commit and working tree, etc |
+| git format-patch | Prepare patches for e-mail submission |
+| git apply | Apply a patch to files and/or to the index |
+| patch | apply a diff file to an original |
+
+## Creation
+
+### Git Staged
+
+Add files to staging then get a diff.  
+
+```sh
+git diff --name-only --cached
+
+git diff --cached
+
+# get the patch
+git diff --cached --patch > ./patches/move_test.patch
+```
+
+### Git Stashes
+
+Create patches from stashes.  
+
+```sh
+# list stashes
+git stash list
+
+# patch
+git stash show -p stash@{0} > my_stash.patch
+```
+
+### Diff
+
+```sh
+# -N absent files as empty
+# -a text files
+# -u unified
+# -r recursive
+diff -Naur ./src-directory ./dest-directory
+```
+
+## Applying
+
+Taking patches from a source tree to another.  
+
+### Git
+
+```sh
+# Git Apply
+git apply --ignore-whitespace patches/move_test.patch
+
+# Git Reverting
+git apply -R patches/move_test.patch
+```
+
+### Patch
+
+```sh
+# you can dry run (it's also a cheap way of listing file in the patch)
+patch -p1 --dry-run --force --merge -i patches/fullfile.patch
+
+# applying a patch
+patch -p1 -i patches/move_test.patch   
+
+# Patch Revert
+patch -p1 -R -i patches/move_test.patch 
+
+patch -p1 --force --merge -i patches/fullfile.patch
+```
+
+## Scenarios
+
+### Scenario 1
+
+File is missing in the patch target.  A file that is modified in the source does not exist in the target. 
+
+The patch tool warns that it cannot find the file and it stores a the unapplied patch in a `..rej ` folder.  
+
+### Scenario 2
+
+You want to keep a full file for all new/modified files.  When applying you just want to overwrite the existing files.  
+
+```sh
+# First, find the empty tree's hash
+EMPTY_TREE=$(git hash-object -t tree /dev/null)
+# Then, for each modified file, create a diff against the empty tree
+git diff $EMPTY_TREE your_file > your_file.patch
+```
+
+## Resources
+
+* Generating patch text with -p [here](https://git-scm.com/docs/diff-generate-patch)  
+* Comparing and Merging Files [here](https://www.gnu.org/software/diffutils/manual/html_node/index.html)  
+* Git Diff and Patch – Full Handbook for Developers [here](https://www.freecodecamp.org/news/git-diff-and-patch/)