Scalar Data

• A scalar is the simplest kind of data that Perl manipulates
  • String of characters
  • primatives
• Numbers
  • Perl always uses double-point precision for values (no difference between floats or integers)
  • Examples:

#Numbers
 $myint1 = 123456; 
 $myint2 = 123_456; # can use _ anywhere in number
 $mybig1 = 1.23e10; # e notation
 $mysmall1 = 0xff; # hex notation
 print "$myint1 \n$myint2 \n$mybig1 \n$mysmall1 \n"; 
 #Output:
 #123456
 #123456
 #12300000000
 #255

#Arithmetic
$ans = 2 + 3 # 5

$ans = 5.1 – 2.4 # 2.7

$ans = 3 * 12

$ans = 14 / 2

$ans = 7 % 3 # 1 (modulus)

$ans = 7 ** 3 # 343 (exponential, 7^3)

• Strings
  • Sequence of characters from “” to “max memory” – Perl has no built-in limit for strings
  • Can come in two different types: ‘Single Quoted String’ vs “Double Quoted String”
  • ‘Single Quoted’
    • Any string within the quotes stand for itself (except the single quote character, which would terminate this string)

'hello\n' # hello + newline character
 'hello
 there' # hello + newline + there
 'don\'t forget' # don't forget # the \' is needed to continue this string to the end

• • “Double Quoted”
    • The backslash takes its full power definition, such as tab and newline characters

"hello world \n" # hello world + newline
 "coke\tsprite" # coke + tab + sprite

• • String Operators
    • Concatenation is . (period)
    • String repetition is done using the x character

"fred" x 3 # "fredfredfred"
 5 x 3.7 # "555" The "5" is converted to string and "3.7" is truncated to "3"
 "cat" x .7 # "" empty string result due to truncation

• • Generally Perl does all numbers / strings conversions by acknowledging the situation
    • Checks operators to determine what data types are expected
    • Does type conversions on the fly, some exceptions:

"Z" . 5*7 # "Z35" this results in Z concatenated to the result of 5*7
 "12fred" * " 3" # "36" the "fred" is truncated as the "*" operator requires number

• Perl Warnings
  • When running perl programs, give the “-w” option to view warnings

$ perl -w my_program.pl

• • Or include the option in the header of the program file

#!/usr/bin/perl -w 
 use warnings; # two other ways to turn on warnings

• Scalar Variables
  • A scalar variable holds a single scalar value, and is begins with $ in the variable name
  • Scalar variables in always preceded with $ (sigil)
  • Binary Assignment Operators

    • $myvar += 1; incremental

    • $str .= "\n"; concat at string end

  • Interpolation
    • Any variable within a string with double quotes is replaced with its value

print “fred at $n ${what}s. \n”;

print “fred at $n $what” . “s. \n”; #both these lines output the same

• Operator Precedence – Order from highest to lowest:
  • Left to right
  • Parentheses
  • Auto incrementation/decrements (++/–)
  • Exponent **
  • Arithmetic
• Comparison Operators
  • Have both characters and words to do the comparisons. Table:

Equal	==	eq
Not Equal	!=	ne
Less than	<	lt
Greater than	>	gt
Less or equal	<=	le
Greater or equal	>=	ge

• IF control

If ($name gt ‘fred') { print "here"; }
 Else { print "there"; }

• IF control with Boolean values

$result = $name gt ‘fred';
 If ($result) {...}

• • For numbers, any value other than zero is true, zero is always false
  • For strings, empty string is false, anything else is true
  • Exception for strings # “0” is actually the save value as number zero so it is the only non-empty string that will result in false
• Getting User Input
  • Easiest way is using <STDIN>

$line = <STDIN>;
 print "Input was: $line \n";

• Chomp operator
  • Function with return value – returns the number of characters removed, returns zero if nothing is chomped
  • Removes all trailing newline characters
  • Can be called with or without parentheses

chomp ($text = <STDIN>);
 $result = chomp $variable;

• The while Control Structure

$count = 0;
 while ($count < 10) { … $count += 1; … }

• The undef Value
  • This is a scalar value all on its own, defaults to zero or empty string

$sum += 1; # sum = 1
 $string .= “hello world”; # string = hello world

• The defined Function
  • Used to check undef variables

if(defined($variable)){
 print “True!”;
 } else { print “False!”; }