Adding cd.md for pull request

_commands/basics/cd.md

@@ -0,0 +1,89 @@
+---
+---
+
+cd
+-------
+
+cd allows the user to change their working directory
+
+~~~ bash
+cd eecs398
+cd wk06
+cd advancedhw
+~~~
+If the user started in home and executed these three commands,
+pwd would output "~/eecs398/wk06/advancedhw"
+
+<!--more-->
+
+### Useful Options / Examples
+
+There are multiple shortcuts that can be used with cd:
+
+
+#### Option .
+
+"." represents your current directory
+
+__Usage__:
+`cd ./<subdirectory>`
+
+__Functionality__:
+Can be used to limit typing when you are "deep" in your system
+For example, if you wanted to move a file from
+`~/eecs398/wk06/hw`
+down to
+`~/eecs398/wk06/hw/problem1`
+you could just go to the hw directory and use 
+`mv <filename> ./problem1`
+When using cd, omitting the "." will do the same thing, i.e. you can
+cd into directories in your working directory with just their names
+
+
+#### Option ..
+
+".." represents the directory containing your current directory
+
+__Usage__:
+`cd ..`
+
+__Functionality__:
+Moves "up" one directory, changes your working directory to the directory 
+containing your current directory 
+This also works for longer paths, so if you are in 
+`~/eecs398/wk06/advancedhw`
+and you want to go to 
+`~/eecs398/wk06/hw`
+you can just use
+`cd ../hw`
+
+
+#### Option ~
+
+"~" represents your home directory
+
+__Usage__:
+`cd ~`
+
+__Functionality__:
+This takes you all the way back to your home directory
+Allows you to accomplish multiple iterations of "cd .." in one command
+Omitting the ~ will do the same thing, i.e. cd without a command will 
+default to the home directory
+
+
+#### Option -
+
+"-" represents the previous working directory
+
+__Usage__:
+`cd -`
+
+__Functionality__:
+Returns you to you previous working directory
+This allows you to switch back and forth between directories
+that are "far apart".  If you are in
+`~/eecs398/wk06/advancedhw`
+and you use "cd ~", you will be in your home directory.  If you then
+use "cd -", you will be back in 
+`~/eecs398/wk06/advancedhw`