update

technology/applications/cli/system/Core Utils.md

@@ -31,6 +31,13 @@ Usage: `cat [OPTION]... [FILE]...`
 | `-b, --number-nonblank` | number nonempty output lines, overrides `-n` |
 | `-n, --number`          | number all output lines                      |
 
+## cd
+change current working directory
+Usage: `cd [dir]`
+Go to home directory of current user: `cd`
+Go up to the parent of the current directory: `cd ..`
+Go to the previously chosen directory: `cd -`
+
 ## chmod
 change file mode (permissions) bits
 Usage: `chmod [OPTION]... OCTAL-MODE FILE...`