Add PID Of The Current Shell as a unix til

README.md

@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_424 TILs and counting..._
+_425 TILs and counting..._
 
 ---
 
@@ -386,6 +386,7 @@ _424 TILs and counting..._
 - [List All Users](unix/list-all-users.md)
 - [Only Show The Matches](unix/only-show-the-matches.md)
 - [Partial String Matching In Bash Scripts](unix/partial-string-matching-in-bash-scripts.md)
+- [PID Of The Current Shell](unix/pid-of-the-current-shell.md)
 - [Repeat Yourself](unix/repeat-yourself.md)
 - [Saying Yes](unix/saying-yes.md)
 - [Search History](unix/search-history.md)

unix/pid-of-the-current-shell.md

@@ -0,0 +1,23 @@
+# PID Of The Current Shell
+
+`$` expands to the process ID of the shell. So, you can see the PID of the
+current shell with `echo $$`.
+
+```bash
+> echo $$
+36609
+
+> zsh
+
+> echo $$
+45431
+
+> exit
+
+> echo $$
+36609
+```
+
+See the `Special Paramaters` section of `man bash` for more details.
+
+[source](http://stackoverflow.com/questions/21063765/get-pid-in-shell-bash)