CSC295 2014S, Class 02: Some Basic Tasks and Corresponding Tools
================================================================

_Overview_

* Preliminaries.
    * Admin.
* Fun with GitHub.
* Go over homework.
* Exercise: The spaces problem.
* Raymond, chapter 1.
* Thinking about basic tools.

Preliminaries
-------------

### Admin

* I encourage you to attend CS table on Friday and talk about the ACM
  code of ethics.
* Status check 1: How many of you know the C bitwise operations?
  (`&`, `|`, etc.)
* Status check 2: Could anyone *not* make class if I moved it to 3:15pm?
  (Hands closed, blackball-style question.)
    * We are sticking with 1:15 p.m.
* Note: I was overly optimistic at the start of the semester.  Given the
  amount of time daily homework is taking in my three classes, I probably
  won't get a lot of chance to write the "book" for this class.  I will
  try to set up some lab problems, though.

### Questions

Fun with GitHub
---------------

* What happens when someone sends a pull request?
    * GitHub sends you a nice message with instructions.
    * You can browse the request to see how someone wants to screw up the
      repository.
* Isn't our site lovely?
    * Careful instructions and agreed-upon policies help

Go over homework
----------------

### That fun hypothetical C problem.  (Did anyone write code to cause 
the error?)

    int *x;     // Our array of data.
    int 
    main (int argc, char *argv[])
    {
      x = malloc (...);      
      foo ();
      bar ();
      free (x);   // Crash
    } // main

* Multi-threaded program, foo or bar accesses x after it should.
    * foo and bar have terminated.
* malloc keeps track of how much space it has allocated
* Note: "You went beyond the null at the end of the array."
    * Arrays are not null terminated in C.
    * Strings *are* null terminated.

    char *str = malloc (sizeof (char) * 16);
    strcpy (str, "hello");
    printf ("%d\n", strlen (str));

### Spell checking

* Finding information, mechanism one: Google
* Check the manual pages `man -k spell` 
    * The -k is "keyword"
* So, our first solution is to use spell, but it gives us duplicates.
  What next?
    * Read the manual page
    * Use `uniq` - not quite
* spell file | sort | uniq

### URL extraction

    grep -i -o '<img[^>]*src=[^>]*>' input | grep -o '"[^"]*"'

The first part gets you lines that look like
 
   <img ... src=.... ...>

The second part extracts the stuff in quotation marks

Flaws in this solution?

* What if there are other things in quotation marks?  Those get printed too.  Boo.
    * grep -o 'src="[^"]*"' | sed -e 's/^.*src="//' | sed -e 's/".*$'//'
* What if there are multiple images on the same line?  Works okay.
* What if the thing in quotation marks has a greater-than sign?  (Questionable HTML.)  Punt.
* What if the image is in single quotes rather than double quotes?

### The CSV Problem

"I want the names of the people with the five highest grades on HW2."
File has 

    fname:lname:assignment:grade

* grep to find the lines that contain HW2
* sort to put them in numeric order (sort -k4 -n -r)
* cut to remove columns
* head to take the top 5

Exercise: The spaces problem
----------------------------

        sed -e 's/ *$//'

Write it in C.   You have ten minutes.

   While input characters remain
     read the next input character
     switch (ch)
       case space:
         shove it in the buffer
         break;
       case newline:
         clear the buffer
         break;
       default:
         print the buffer
         clear the buffer
         print ch;
         break


Raymond, chapter 1
------------------

Thinking about basic tools
--------------------------

Homework
--------

0. Learn Markdown so that we can use it for these assignments.

1. Learn about how you set and get environment variables.  Put your
explanations in the `submissions` directory, with a file named after
you.

    * Command line
    * Bash
    * C (get only)

2. Update our list of "things every *nix user should know" (either
in the repo

3. Come up with two or three tasks, similar to those we did for assignment
1, and put notes about them in the tasks directory.  (You can include
some sample solutions in your file.)

4. Read the first chapter of the Make book.