Change the zsh heading to unix.

unix/create-a-file-descriptor-with-process-substitution.md

@@ -0,0 +1,23 @@
+# Create A File Descriptor with Process Substitution
+
+Process substitution can be used to create a file descriptor from the
+evaluation of a shell command. The syntax for process substitution is
+`<(LIST)` where `LIST` is one or more bash commands.
+
+```
+$ cat <(echo 'hello, world')
+hello, world
+```
+
+This is particularly useful for commands that expect files, such as diff:
+
+```
+$ diff <(echo 'hello, world') <(echo 'hello, mars')
+1c1
+< hello, world
+---
+> hello, mars
+```
+
+Sources: [Brian Dunn](https://twitter.com/higgaion) and
+[Bash Guide for Beginners](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_03_04.html#sect_03_04_07)