Perl Variables: Array Web Programming1

Review: Perl Variables Scalar ► e.g. $var1 = “Mary”; $var2= 1; ► holds number, character, string Array ► = (“Mary”,”Tom”); ► holds a list of scalars ► $array1[0]=“Mary”; $array1[1]=“Tom”; Associative array (i.e. hash) ► e.g. %hash1 = (“Mary”,”F”,”Tom”,”M”); ► holds key-value scalar pairs ► $hash{“Mary”}=“F”; $hash{“Tom”}=“M”; Web Programming 2

Array and List List ► a sequence of scalar values (i.e. elements) e.g. (1, 2, 3), (“a”, ”b”, ”c”), (1, ”a”, 2.3, 4) Array ► a Perl variable that holds a list data = (1, 2, 3); ► an array element is a scalar variable e.g. $array[0]; Web Programming 3

Array Syntax Array Name ► first character must ► second character must be a letter. ► can consist of only letters, digits, or underscore ► case-sensitive ► can be as long as you want (within reason) Array Elements ► $array_name[$index] ► array index goes from 0 to (array length -1) = (“cat”, ”dog”, “pig”); $array[0] is “cat”, $array[1] is “dog”, $array[2] is “pig” array length ► number of elements in an array ► $array_length Web Programming 4

Array: Value Assignment Assigning values to an array variable = (element0, element1,..); ► an element can be a constant, a variable, an expression, or a list range e.g. 1..5, “a”..“z” ► = (“one”, 2, “three”, “four”, = (1, = (1, 1+1, $a.$b, = = ( ) Array values in a conditional expression ► if false if a null array, true otherwise  Example scriptExample script Web Programming 5

Array Elements array element ► $array[index] index of the last element ► 1 less than array length ► $#array last element ► $array[-1] ► $array[$#array] ► Web Programming 6

Printing Arrays ► prints all elements concatenated together. ► print prints elements separated by a space (default list separator). the list separator ($”) can be set to a different value. ► foreach $item { print “$item\n”; } ► For ($i=0; $i <=$#array; $i++) { print “$array[$i]\n”; }  Example scriptExample script Web Programming 7

String to Array Conversion $string = join ► concatenates elements using $separator $string = ► concatenates elements using “ = split (/$separator/, $string); ► splits $string by $separator  Example scriptExample script Web Programming 8

Array = sort ► sorts = reverse ► reverses the order of array elements $first = shift ► remove and return the first element $last = pop ► remove and return the last element unshift $item); ► add $item to the start push $item); ► add $item to the end chop ► chops the last character of each element chomp ► removes the last character of each element if it is a newline character  Example scriptExample script Web Programming 9

Reading Input into Arrays Reading from STDIN = ;  Example scriptExample script Reading from a file ► reading line by line $line = ; ► reading all at = ;  Example scriptExample script Web Programming 10

Advanced I/O Command line arguments holds command line arguments e.g. prog1.pl arg1 holds (arg1, arg2)  Example scriptExample script Working with a directory ► Open a directory opendir (IND, $directory); ► Read the = readdir (IND); ► Close the directory closedir (IND);  Example scriptExample script Web Programming 11