Adding shell cheat sheet

bash/novice/index.md

@@ -25,6 +25,7 @@ Topics
 See Also
 --------
 *   [Instructor's Guide](guide.html)
+*   [Reference](reference.html)
 
 Resources
 ---------

bash/novice/reference.md

@@ -0,0 +1,53 @@
+---
+layout: lesson
+root: ../..
+title: Shell Reference
+level: novice
+---
+Basic Commands
+--------------
+*   `cat` displays the contents of its inputs.
+*   `cd path` changes the current working directory.
+*   `cp old new` copies a file.
+*   `find` finds files with specific properties that match patterns.
+*   `grep` selects lines in files that match patterns.
+*   `head` displays the first few lines of its input.
+*   `ls path` prints a listing of a specific file or directory; `ls` on its own lists the current working directory.
+*   `man command` displays the manual page for a given command.
+*   `mkdir path` creates a new directory.
+*   `mv old new` moves (renames) a file or directory.
+*   `pwd` prints the user's current working directory.
+*   `rm path` removes (deletes) a file.
+*   `rmdir path` removes (deletes) an empty directory.
+*   `sort` sorts its inputs.
+*   `tail` displays the last few lines of its input.
+*   `touch path` creates an empty file if it doesn't already exist.
+*   `wc` counts lines, words, and characters in its inputs.
+*   `whoami` shows the user's current identity.
+
+Paths
+-----
+*   `/path/from/root` is an absolute path.
+*   `/` on its own refers to the root of the filesystem.
+*   `path/without/leading/slash` is a relative path.
+*   `.` refers to the current directory, `..` to its parent.
+*   `*` matches zero or more characters in a filename, so `*.txt` matches all files ending in `.txt`.
+*   `?` matches any single character in a filename, so `?.txt` matches `a.txt` but not `any.txt`.
+
+Combining Commands
+------------------
+*   `command > file` redirects a command's output to a file.
+*   `first | second` connects the output of the first command to the input of the second.
+*   Use a `for` loop to repeat commands once for every thing in a list:
+
+        for variable in name_1 name_2 name_3
+        do
+            ...commands refering to $variable...
+        done
+
+*   Use `$name` to expand a variable (i.e., get its value).
+*   Use `history` to display recent commands, and `!number` to repeat a command by number.
+*   Use `bash filename` to run commands saved in `filename`.
+*   `$*` refers to all of a shell script's command-line parameters.
+*   `$1`, `$2`, etc., refer to specified command-line parameters.
+*   Use `$(command)` to insert a command's output in place.