Add Copying Nested Directories With Ditto as a unix til

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/).
 
-_857 TILs and counting..._
+_858 TILs and counting..._
 
 ---
 
@@ -756,6 +756,7 @@ _857 TILs and counting..._
 - [Command Line Length Limitations](unix/command-line-length-limitations.md)
 - [Configure cd To Behave Like pushd In Zsh](unix/configure-cd-to-behave-like-pushd-in-zsh.md)
 - [Copying File Contents To System Paste Buffer](unix/copying-file-contents-to-system-paste-buffer.md)
+- [Copying Nested Directories With Ditto](unix/copying-nested-directories-with-ditto.md)
 - [Create A File Descriptor with Process Substitution](unix/create-a-file-descriptor-with-process-substitution.md)
 - [Curling For Headers](unix/curling-for-headers.md)
 - [Curling With Basic Auth Credentials](unix/curling-with-basic-auth-credentials.md)

unix/copying-nested-directories-with-ditto.md

@@ -0,0 +1,47 @@
+# Copying Nested Directories With Ditto
+
+You can copy nested directories with `cp` using the `-R` (_recursive_) flag.
+The way `cp` works is that it replaces the target location with the source
+directory, wiping out whatever files or directories reside at the target
+location.
+
+Conversely, the `ditto` utility, available on OS X's version of Unix, does
+_recursive_ directory copies by default and merges the contents of any existing
+directories.
+
+As an example, here are two folders, `folder1` and `folder2`:
+
+```bash
+❯ exa -T folder1
+folder1
+├── cats
+│  └── sneaky
+└── dogs
+   └── fido
+
+❯ exa -T folder2
+folder2
+└── cats
+   └── oreo
+```
+
+Using `ditto` to copy `folder1` to `folder2`
+
+```bash
+❯ ditto folder1 folder2
+```
+
+we get a `folder2` where directories from `folder1` are created and existing
+directories are merged together.
+
+```bash
+❯ exa -T folder2
+folder2
+├── cats
+│  ├── oreo
+│  └── sneaky
+└── dogs
+   └── fido
+```
+
+See `man ditto` for more details.