CS 368-1 (2011 Summer) — Day 9 Homework

Due Tuesday, July 26, at the start of class.

Description

Read a Perl script as input, and do two things:

• Report some statistics about the code
• Fix some formatting problems in the code and save your new version

Details

The script takes the name of a Perl script as input: You can ask the user for the filename or simply hard-code it into your script. It will also save a new version of the Perl script: Either hard-code the new filename into your script or (more advanced) modify the given input filename to include “-new” right before the “.pl” extension.

Code Statistics

We would like to report on the code itself. Implement at least two of the following reports (arranged very roughly in order of easiest to hardest):

• Lines of code: Count “real” lines of code. Do not count blank lines or lines that contain only a comment. For example, the following code contains only two “real” lines of code:

  # Get user input
  my $line = <STDIN>
          
  # Remove trailing newline
  chomp($line);

• Subroutine names: List all of the subroutines that are defined in the script. That is, look for lines with the sub keyword and the subroutine name. Only keep the subroutine name. Assume that the sub keyword and the subroutine name are on the same line, but that the opening curly brace ({) may or may not be on the same line. Where can whitespace occur?
• Comment blocks: Count the number of comment blocks, where a comment block is defined as a set of consequetive comment lines. For example, the following code has three comment lines total, but only two comment blocks:

  sub get_input {
      # Loop until we get valid input.
      # Valid means non-empty.
      while (1) {
          chomp (my $input = <STDIN>);
          # Check for valid input
          return $input unless $input eq '';
      }
  }

• Scalar variable names: List all of the scalar variables that are defined or used in the script. Remember that all scalars begin with a dollar sign ($), but not every expression that begins with a dollar sign includes the name of a scalar variable. For example, look at the following code:

  my $foo = 1;
  my @array;
  $array[$foo] = 'hello';

  In that sample, foo is a scalar variable name, but array is not, even though $array occurs in the third line.

  Hint: Remember the definition of the “word” character class in Perl regular expressions?

• Arrays and hashes: Same as the last item, but include array and hash variable names, too. But, list the names of each type of variable separately — scalars, arrays, and hashes.

Fixing the Code Format

Everyone makes mistakes formatting their code now and then. The script will fix certain formatting mistakes and save the new, rewritten version of the code to a file. Implement at least one of the following fixes (again, arranged very roughly in order from easiest to hardest):

• Spacing around operators: It is considered good coding style to put a single space character on either side of operators like “=”, “+”, and so forth. For a reasonable subset of operators (say, at least 5 or so), fix the input Perl code to have the proper spacing. Be sure that you do not insert a space inside of two-character operators like “+=”. Also, it is OK if your code changes the spacing around operators that happen to occur within comments and quotes.
• Enforce use of strict and warnings: Make sure that the script contains the “use strict” and “use warnings” directives. If they are absent from the script, put them at the top, after any “#!” line.
• Rewrap comment blocks: This is fairly hard… For each comment block in the script, assume that the first line is indented correctly, gather all of the real text of the comment block (i.e., not the leading “#”) and rewrap the text into one or more lines that come as close to but do not go beyond a given column in your code file (column 80 is a good starting point).

  Look at the standard Text::Wrap module for significant help with this modification. However, even using the module, this task is hard.

• Make your own! If you have an idea for an interesting, non-trivial formatting fix, go ahead and (a) describe it clearly in a comment block in your code, and (b) implement it.

Note: In practice, I would not really do this to Perl code, because there are always reasonable exceptions to code formatting rules. But it’s good practice…

Example Output

A sample of the report output is below (taken from my solution to Homework #5).

Lines of Code:     51
Subroutine Names:  convert, get_number, get_unit
Scalar Names:      character, from_unit, i, length, meters, ok, result, to_from, to_unit, unit, units, value

Hints

Repeated Matches

You may want to match every instance of a pattern in a single string. How do you loop through them? It is much like doing repeated substitutions, use the g modifier:

while ($string =~ /...(...).../g) {
    # do something with each match within $string
}

Reminders

Do the work yourself, consulting reasonable reference materials as needed; any reference material that gives you a complete or nearly complete solution to this problem or a similar one is not OK to use. Asking the instructors for help is OK, asking other students for help is not.

Hand In

A printout of your code on a single sheet of paper (if possible). Be sure to put your own name in the initial comment block of the code. Identifying your work is important, or you may not receive appropriate credit.