CSCI 3294 (Unix Power Tools), Fall 2010:
Homework 2

Credit:

40 points.

Reading

Read about the following topics in the list of suggested readings, either in one of the suggested readings or in another book or reference. (These are the topics for September 8, September 13, and September 15.)

• Shell basics and customizations.

• I/O redirection and pipes.

• Filter programs and other useful commands.

(Notice that questions below are grouped by topic, so you can read about one topic, do the related questions, and then move on to the next topic.)

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 my mailbox in the department office. 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 Fedora Linux 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. You might be constrained by the capabilities of aliases versus functions.)

   Notice 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.

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. For most-accurate results, you probably need to run this on the machine on which accounts are created.)

2. (5 points) What would you type at the command line to find all files in your home directory (and all subdirectories) that are less than a day old and end with .c?

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.

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?

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, find a Janus 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.