CSCI 3294 (Seminar: UNIX Power Tools), Fall 2018:
Homework 2

Credit:

40 points.

Reading

Be sure you have read, or at least skimmed, the assigned readings for 9/05 and 9/10.

Problems

Answer the following questions. You may write out your answers by hand or using a word processor or other program, but please submit hard copy, either in class or in one of my mailboxes (outside my office or in the ASO). Answers to most questions will involve experimentation on a UNIX or Linux system. You are free to use any appropriate system (unless a specific problem says otherwise); if you use something other than one of our classroom/lab machines please tell me what.

Shell basics and customizations

(Answer the following questions for the bash shell.)

1. (5 points) When you type a command (e.g., ls), the shell has to find an executable (program) to run. Where does it look? How could you make it also look in your directory MyPrograms (in addition to wherever it looks now)? How could you make it look only in your directory MyPrograms?

2. (5 points) Give the command(s) you would use to define two aliases or shell functions: delete to move a file to be ``deleted'' to a temporary directory such as $HOME/.trash, and undelete to move a ``deleted'' file from the temporary directory to the current directory. (Examples of use: delete myfile, undelete otherfile.)

   (It's up to you to decide whether these should be aliases or shell functions. Hint: You might be constrained by the capabilities of aliases versus functions.)

   Note that commands to define aliases or functions can be entered from the command line, in which case they apply to the current session only, or can be included in an appropriate initialization file.

I/O redirection and pipes

1. (5 points) How would you invoke the gcc compiler if you want to be able to page through its output (both standard output and standard error) with less?

   How would you capture the error output only in a file called gcc-ERRORS?

2. (5 points) How could you make a one-line text file without using a text editor? Could you extend this idea to make a multiline text file? Tell me about as many ways to do this as you can think of.

Filter programs and other useful commands

1. (5 points) When a new user account for the department's lab machines is created, part of the setup procedure is to create a home directory in /users and copy into it certain files from /etc/skel. What command could you use to compare the files in your home directory to the files in /etc/skel (including any files in subdirectories), for example to find out whether you had inadvertently changed or deleted something that might be important? (Hint: You can do this with one command.)

2. (5 points) What would you type at the command line to find all files in your home directory (and all subdirectories) that have been modified within the past 24 hours and end with .c?

3. (5 points) What would you type at the command line to get a sorted list, with no duplicates, of all the users running processes on the machine you're using, along with a count of processes they're running?

4. (5 points) Answer/do one of the following:
   1. What would you type at the command line to find out how many processes are being run by user root?

   2. Describe something you actually want to do (e.g., archive all files that have been changed in the last 24 hours, or find a classroom machine that's up and connect to it with ssh) and a solution involving a pipe and at least one of the commands mentioned in the reading for this assignment.

Honor Code Statement

Include the Honor Code pledge or just the word ``pledged'', plus at least one of the following about collaboration and help (as many as apply).¹Text in italics is explanatory or something for you to fill in. For programming assignments, this should go in the body of the e-mail or in a plain-text file honor-code.txt (no word-processor files please).

• This assignment is entirely my own work. (Here, ``entirely my own work'' means that it's your own work except for anything you got from the assignment itself -- some programming assignments include ``starter code'', for example -- or from the course Web site. In particular, for programming assignments you can copy freely from anything on the ``sample programs page''.)
• I worked with names of other students on this assignment.
• I got help with this assignment from source of help -- ACM tutoring, another student in the course, the instructor, etc. (Here, ``help'' means significant help, beyond a little assistance with tools or compiler errors.)
• I got help from outside source -- a book other than the textbook (give title and author), a Web site (give its URL), etc.. (Here too, you only need to mention significant help -- you don't need to tell me that you looked up an error message on the Web, but if you found an algorithm or a code sketch, tell me about that.)
• I provided help to names of students on this assignment. (And here too, you only need to tell me about significant help.)

Essay

Include a brief essay (a sentence or two is fine, though you can write as much as you like) telling me what about the assignment you found interesting, difficult, or otherwise noteworthy. For programming assignments, it should go in the body of the e-mail or in a plain-text file essay.txt (no word-processor files please).

Footnotes

... apply).¹

Credit where credit is due: I based the wording of this list on a posting to a SIGCSE mailing list. SIGCSE is the ACM's Special Interest Group on CS Education.