1. Perl Variables: Array
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2. 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”;
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3. Array and List List Array 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];
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4. Array Syntax Array Name Array Elements array length
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
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5. Array: Value Assignment
Assigning values to an array variable
@array = (element0, element1, ..);
an element can be
a constant, a variable, an expression, or
a list range e.g , “a”..“z”
e.g.
@array = (“one”, 2, “three”, “four”, 5)
@array = (1, $a,
@array = (1, 1+1, $a.$b, 1..5)
@array = (1)
@array = ( )
Array values in a conditional expression
if false if a null array, true otherwise
Example script
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6. Array Elements array element index of the last element in @array
$array[index]
index of the last element
1 less than array length
$#array
last element
$array[-1]
$array[$#array]
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7. Printing Arrays print @array; print “@array”;
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 script
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8. String to Array Conversion
$string = join
concatenates elements using $separator
$string =
concatenates elements using “ ”
@array = split (/$separator/, $string);
splits $string by $separator
Example script
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9. Array Functions @array2 = sort (@array); @array2 = reverse (@array);
sorts alphabetically
@array2 = 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 script
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10. Array Functions Insert elements Replace elements Remove elements
@array2 = splice offset, length);
Remove elements (length from offset)
@array2 holds the removed elements
$array2 = splice offset, length);
$array2 holds the last removed element
@array2 = splice offset);
Remove elements (from offset to end of the array)
Insert elements
splice offset, 0, LIST);
Insert LIST at offset
No return value
Replace elements
@array2 = splice offset, length, LIST);
Remove elements (length from offset) & Insert LIST at offset
Example script
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11. Reading Input into Arrays
Reading from STDIN
@array = <STDIN>;
 Example script
Reading from a file
reading line by line
$line = <FILE>;
reading all at once
@lines = <FILE>;
Example script
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12. Advanced I/O Command line arguments Working with a directory
@ARGV holds command line arguments
e.g. prog1.pl arg1 arg @ARGV holds (arg1, arg2)
 Example script
Working with a directory
Open a directory
opendir (IND, $directory);
Read the contents.
@files = readdir (IND);
Close the directory
closedir (IND);
Example script
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