Intro to Perl - Day 3

Goals

• Use special printing functions
• Use perl's report formatting
• write reusable code in subroutines
• become familiar with perl variable scope

Review

POST

1. which special variable contains command-line arguments?
2. what is the difference between ++$a and $a++
3. what does keys() do?
4. when do you use each versus foreach
5. what is the difference between @_ and $_ ?

Use special printing functions

• printf("[control string]", [list of vars]);

  
  format: %m.nx, where x is one of:
  
  c	character
  d	decimal integer (base 10)
  e	exponential float
  f	float
  g	compact float
  ld	long decimal
  lo	long octal
  lu	long unsigned decimal
  lx	long hex
  o	octal
  s	string
  u	unsigned decimal
  x	hex
  

• sprintf([control string], [list], returns a string rather than printing it.

Use perl's report formatting

1. define format (template, fieldlines, valuelines, fieldholders) p120-123

   
   format [leave at default, or use a NAME] =  UC, default if not named
   Hello, my name is @<<<<<<<<<<    field holder w/11 left-justified places
   $name valueline related to fieldline above
   My pencil is @<<<<<<<<<< and @>>>>  right-just, too
   $pencil_color,		     $pencil_size  lined up for humans
   . 1st column, on line by itself, like here-doc terminator 
   

2. load up variables for printing
3. invoke the format: write;

write reusable code in subroutines

1. write the subroutine

   
   sub addem 
   {
   my($first_num, $second_num)=@_; #grab the results of the default array 
   				#before it gets changed.
   						
   				#if you pass an @array, it must be the
   				#the last argument passed, or a greedy @array
   				#on the receiving end will eat it all, leaving
   				#nothing for subsequent vars in the list
   				#ex, ($var, @array) not (@array, $var)
   				#see p51	
   
   my($sum)= $first_num + $second_num;
   return $sum;
   
   # or just return ($first_num + $second_num);
   
   }#end, addem
   
   $total=&addem(4,5);	#if passing strings use quotes
   #or $total=&addem($some_num, $another_num);# already set values	
   #or $total=&addem(@nums); #already said that @nums=4, 5;
   

an actual example:

sub assignInput
	{
	#capture arguments
	local($line,$delimiter,@definition)=@_;

	#set local hash to hold data
	local(%filled);

	#strip off linefeed, if applicable 
	chomp($line); 
		    
	#split out line from input
	local(@separated) = split(/$delimiter/ ,$line);
			       
	#make association between @definition and the %hash to be returned
	while ($counter=0; $counter<=$#definition; $counter++)
		{
		$filled{ $definition[$counter] }=$separated[$counter];
		}

	#send the %filled hash back to calling program
	return %filled;

Homework