CS 2304--UNIX: Assignment 3

Due Friday, February 28, by 5pm

100 Points

1. Regular Expressions: What Strings Match an RE?

Consider the following text, taken from the manual page for a command called "flip" (if you would like to use flip, you can find it compiled for FreeBSD along with it's man page in the directory ~sedwards/bin on the lab machines):

Flip is a file interchange program that converts text file
formats between **IX and MS-DOS.  It converts lines ending
with carriage-return (CR) and linefeed (LF) to lines ending
with just linefeed, or vice versa.

1. /file/
2. /^f/
3. /^[Ff]/
4. /./
5. / */
6. /line\(s\)?/
7. /convert|change/
8. /[Cc].*[Rr]/
9. /text.*file/
10. /[a-z][a-z]*ing/

If you are unsure about a question, feel free to try out a few experiments with egrep or with the "Search" menu in emacs. Remember that neither of these programs expect you to enter the "/" delimiters when you type the RE for which to search. Also, note that emacs normally ignores case in searches by default.

2. Regular Expressions: What Strings Match an RE? (cont.)

For the next set of REs, identify all substrings that match each RE (without crossing lines, of course) in the four lines listed in Section 1. You can do this by underlining all matches. For example, the RE /(.*)/ matches the following:

Flip is a file interchange program that converts text file
formats between **IX and MS-DOS.  It converts lines ending
with carriage-return (CR) and linefeed (LF) to lines ending
                     ----              ----
		     ----------------------
with just linefeed, or vice versa.

1. /[Ff][^ ]*/
2. /line[a-z]*/
3. /c.*r/
4. /text/
5. /\*+/

3. Regular Expressions: Writing REs

Now it is your turn to write some REs to match specific text fragments. For each of the following questions, write an RE that matches the specified text (including but not limited to all of the underlined phrases in each example):

1. Matching "hello", "hi", or "howdy":

   hello, there.  or is "hi" or "howdy" more to your liking?
   -----                 --      -----
   

2. Matching "the", regardless of case:

   The quick brown fox jumps over the lazy dog.
   ---                            ---
   

3. The last word in a sentence:

   How many sentences are here? There are two.  No, three!
                          -----           ----      ------
   

4. A social security number:

   The number 045-35-2344 is a random SSN.
              -----------
   

5. A word with five or more letters:

   This sentence does not have many long words.
        --------                         -----
   

6. Any word beginning with the root "reus":

   reusable software is software that was designed to be reused.
   --------                                              ------
   

7. An entire sentence that ends in a period:

   Does this sentence end in a period?  This one does.
                                        --------------
   

8. Any sequence beginning with "artificial" and ending with "intelligence":

   Politicians can act artificial, but do they have intelligence?
                       -----------------------------------------
   

9. Any of "computer", "computers", or "computing":

   computer science is the study of computing, and how computers work.
   --------                         ---------          ---------
   

10. Matching any phrase of exactly three words separated by white space:

    This is a short sentence.
    ---------
         ----------
            ----------------
    

Submitting Your Answers

You are to hand in your assignment by sending an email message to the address cs2304u@ei.cs.vt.edu. To receive credit, you mail message must be RECEIVED by this account by the time and date listed above. It is your responsibility to successfully submit your assignment via email.

The body of your message must be a plain ASCII text file that contains the following:

• A subject line containing "HW 3", the homework number.
• Your name.
• Your student ID number.
• Answers to all 25 of the above questions on REs:
  • For each of the 10 questions in Section 1, just list the line number(s) for which lines match each RE.
  • For each of the 5 questions in Section 2, show all four lines of the original text, with every possible match underlined (as shown in the examples).
  • For each of the 10 questions in Section 3, show the RE you came up with.
  Do not attach files produced by word processors or other programs--send plain ASCII text only.