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A Brief Introduction to Perl. Part I. A Brief Introduction to Perl. Introduction Scalar Data Variables Operators If-Else Control Structures While Control Structures Standard Input Lists and Arrays. Introduction. Perl 1 - Created by Larry Wall in 1987 Stable Release: Perl 5.10.1.
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A Brief Introduction to Perl Part I
A Brief Introduction to Perl • Introduction • Scalar Data • Variables • Operators • If-Else Control Structures • While Control Structures • Standard Input • Lists and Arrays
Introduction • Perl 1 - Created by Larry Wall in 1987 • Stable Release: Perl 5.10.1
Scalar Data Two basic scalar data types: Numbers and Strings • Numbers • Integers and Floating-Point Numbers have the same format. • Ex. $v=8 #v contains value of 8 • Strings • Sequences of Characters. • Can either be enclosed in single or double quotes. • Ex. $v=“a” #v contains value of “a” Undef – For Numbers or Strings, there is a special value called undef. This is initially assigned to all variables and acts as a zero for numbers and a null or empty string for strings.
Variables • A scalar variable holds a single scalar value • Names of any scalar variable must begin with the “$” symbol followed by a Perl identifier Ex. $tom, $cs265
Operators • Assignment • Arithmetic • String • Numeric Comparison • String Comparison
Assignment Operator = Ex. $cs = 265
Arithmetic Operators +, -, *, / Ex. $c = a + b (Addition) $c = a – b (Subtraction) $c = a * b (Multiplication) $c = a / b (Division)
String Operators ., x . (dot) – String Concatenation Ex. $cl = class, $ro = room, $cl . $ro = classroom x – String Multiplier Ex. $cl x 2 = classclass
Numeric Comparison Operators ==, !=, <,>,<=,>= “==” = Equal To “!=” = Not Equal To “<” = Less Than “>” = Greater Than “<=” = Less Than or Equal To “>=” = Greater Than or Equal To
String Comparison Operators eq, ne, lt, gt, le, ge “eq” = Equal To “ne” = Not Equal To “lt” = Less Than “gt” = Greater Than “le” = Less Than or Equal To “ge” = Greater Than or Equal To
Two Special Features of Perl • 1. Interpolation of scalars into strings • Any scalar variable inside a double quoted string is replaced by its value. • Ex. $example=“example”; print "$example"; prints example • 2. Automatic conversion between numbers and strings • Arguments of an arithmetic operator are automatically recognized as numbers, and arguments of a string operator as strings. • Ex. $one = 1, $two = 2.. • print $one*$two; prints 2 • print $one x $two; prints 11 • print $one . $two prints 12
If-Else Control Structures Conditional Loop if(…){ … } else { … }
Example: If-Else Control Structure $expected = “apple”; $given = “pear”; if($expected eq $given){ print “Apple” } else { print “Other Fruit” }
While Control Structure Conditional Loop while (…) { … }
Example: While Control Structure $num = 1; while ($num != 1111) { $num . $num; }
Standard Input • Input in Perl is very convenient • <STDIN> Ex. Typical Line of Code for input $line=<STDIN> # read a full line from standard input and store it in variable $line
Example $line=<STDIN>; if($line eq "\n"){ print "This was an empty line.\n"; } else { print "This line was not empty.\n"; }
Lists • Lists are also user friendly in Perl • List Literals (representations of lists) • Ex. (1,2,3,4) # a list consisting of numbers 1,2,.. 4 • Ex. (1..10) # the same list as the one above, now created by the range operator • ($a ..$b) - the range determined by current values of $a and $b List Assignment Examples:
Arrays • Arrays are variables storing lists. • @num = (1..100) # creates an array “num” with a numbers 1 through 100 • print $num[0] # prints out 1 • print $num[$#num] # prints out the largest index of the array
