CSCI 3294 (Unix Power Tools), Spring 2006:
Homework 5

Assigned:

February 22, 2006.

Due:

March 1, 2006, at 5pm.

Credit:

20 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 February 22):

• Regular expressions.

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 Core Linux please tell me what.

Regular expressions

1. (4 points) Write a grep command to search all the files in the current directory for lines containing either your Linux username (e.g., bmassing) or your last name. (You don't have to also search subdirectories, just files in the current directory itself.)

2. (4 points) Write a grep command to search all files in the current directory for strings that could be Social Security numbers (strings of the form nnn-nn-nnnn, where each n is a decimal digit).

3. (4 points) Suppose you have a Java program in file Foo.java containing the not-very-well-named variable Bar, and you want to change this variable to bar everywhere it occurs, without changing other occurrences of the string Bar (such as myBar or BarFoo). Write a sed command that makes this change. (Note that essentially the same command would work in vim.) Don't worry about saving the output back into the file; the point here is the command to make the change.

4. (8 points) Suppose you have a text file (call it foo) containing a list of names and e-mail addresses. Each line contains first an e-mail address (which for simplicity we'll define as any combination of letters, digits, and periods, followed by a @, followed by any combination of letters, digits, and periods), then some delimiter (a space, a colon, a comma - anything that can't be part of the address as we defined it), and then a name. Write a sed command to reverse the addresses and names, removing the delimiters and leaving at least one space between the name and the address. For example, ``me@mail.com: This Is Me!'' would be changed to ``This Is Me! me@mail.com''. (Hint: Backreferences may be useful.) Again, don't worry about saving the changes back to the file. Also don't worry about what happens to lines that don't have the form described (e.g., no e-mail address), or about pruning out extra spaces.