added a1 skeleton

labs/a1.md

@@ -92,6 +92,10 @@ The `LIST` can either be something like a directory with multiple files or a fil
 ## Useful Commands
 Some commands which could be useful in completing the lab. Of course, there are many approaches to the problems, and using these commands is not required.
 
+### `cat`
+
+`cat` [prints][8] files to the [standard output][7]. Very useful for printing something to pipe into other commands!
+
 ### `cut`
 
 `cut [options] [filename]` extracts certain parts of a file (or piped-in input) based on the [arguments][3] that are used. A few which might be useful: 
@@ -106,6 +110,16 @@ Some commands which could be useful in completing the lab. Of course, there are
 
 `grep [pattern] [filename]` [filters out][4] and returns lines from a file (or piped-in input) that contain the specified pattern.
 
+### `sed`
+
+`sed` can do [many things][9], such as editing strings and matching regex. We can use `sed` to replace one pattern with another pattern as follows:
+
+``` sed 's/<PATTERN-TO-REPLACE>/<NEW-PATTERN>/g <INPUT>' ```
+
+sed` can also take piped-in input from something else instead of an explicit input.
+
+The `g` at the end tells `sed` to replace all ocurrences of the pattern; it can be omitted if we want to replace only the first ocurrence of a pattern, or replaced with a number to replace only a certain number of occurrences.
+
 ### `xargs`
 
 `xargs` lets us apply a command to an output redirected from a pipe. For instance, `output | xargs command` would apply `command` to `output`. Some useful [options][5]:
@@ -195,6 +209,8 @@ $ ls -lAh tmp | grep .txt | wc -l # Gets the number of lines in ls which contain
 26
 ```
 
+**Hint:** Need help looping through files? See this week's participation assignment on [Gradescope][10] for more hints on `for` loops!
+
 for bonus points, instead of using something like `sed` to affect the rename,
 use [shell parameter expansion][1].
 
@@ -238,7 +254,9 @@ $ ls
 ```
 
 **Hints:** 
+- If it's easier, download the above file and work on it in your VM so you don't have to process output from `wget`. 
 - What common text manipulation commands can help you solve this?
+- Consider the commands `cat | grep ___ | cut  ___ | sed ___ | xargs ___` (though you don't *have to* use them...)
 - As always, be aware that there isn't one unique solution to this problem!
 
 Submit your one line solution on Gradescope!
@@ -307,4 +325,8 @@ You may want to look into `dd`[^dd] and the `iflag=fullblock` argument,
 [3]: https://linux.die.net/man/1/cut
 [4]: https://linux.die.net/man/1/grep
 [5]: https://linux.die.net/man/1/xargs
-[6]: https://en.wikipedia.org/wiki/Man_page
+[6]: https://en.wikipedia.org/wiki/Man_page
+[7]: https://linuxhint.com/bash_stdin_stderr_stdout/
+[8]: https://linux.die.net/man/1/cat
+[9]: https://linux.die.net/man/1/sed
+[10]: https://www.gradescope.com/