List-Manipulation Functions

There are two groups of functions that manipulate lists and arrays

Array and List Functions

The following functions manipulate standard array variables and the lists that they store

grep extract the elements of a list that match a specified pattern
splice enables you to modify the list stored in an array variable, by passing appropriate arguments to splice, you can add elements to the middle of a list, delete portion of a list, or replace a portion of a list.
shift remove an item from the beginning a list
unshift put an item at the beginning of a list
push put an item to the end of a list
pop remove an item from the end of a list
split split a character string into a list of elements
sort/reverse sort a list alphabetically
reverse reverse the order of a list
map enables you to use each element of a list, in turn as an operand in an expression
wantarray wantarray determines if the calling function wants a scalar or array variable returned
Examples
grep

# grep (<pattern>, <searchlist>)

$line = "This line of input contains 8, 11 and 26.";
@words = split(/\s+/, $line);

@numbers = grep(/^\d+[.,;:]?$/, @words);
print ("Numbers: @numbers");

Note: you can also use grep with the file-test operators

opendir(CURRDIR, ".") || die("Can't open current directory");
@filelist = grep(!/^\./, grep(-r, readdir(CURRDIR)));
print ("@filelist");

splice

# retval = splice(<array>, <skipelements>, <length>, <newlist>);

# Replace
@array = qw(1 2 3 4);
splice (@array, 1, 2, ("two", "three"));        # list will now be (1 two three 4);

# Appending
splice(@array, 3, 0, "hello", "there");         # add to position 3 shifting anythnig after
splice(@array, @array, 0, "hello", "there");    # add to the end of the list

# Deleting
splice(@array, 2, 2);                           # delete two elements from the offset
shift/unshift

## add or delete from the left side of the array, element 0

@array = qw(1 2 3 4);

$first_element = shift(@array);

print ("Array: @array");
print("\nFirst element:" . $first_element);

unshift(@array, $first_element);
print ("\nArray: @array");
push/pop

## add or delete from the right side of the array, last element

@array = qw(1 2 3 4);

$first_element = pop(@array);

print ("Array: @array");
print("\nFirst element:" . $first_element);

push(@array, $first_element);
print ("\nArray: @array");
split

$string = "one::two::three::four::five::six";
@words = split(/::/, $string);
@limit_words = split(/::/, $string, 3);         # specify a maximum number of elements
print ("@words");
print ("@limit_words");

sort @array = qw( one two three four five six);

@sorted = sort(@array);
print ("@sorted\n");
reverse @array = qw( one two three four five six);

@reversed = reverse(@array);
print("@reversed");
map # map(<expression>, <array>);        # The map function uses the system variable $_ for each element

@array = qw(100 200 300 400);

@results = map($_+1, @array);

print("@results");
wantarray @array = &mysub();                   # using an array the wantarray will return true
$scalar = &mysub();                  # using an scalar the wantarray will return false

sub mysub {
   if (wantarray()) {
      print("Returning type is an array - TRUE\n");
   } else {
      print("Returning type is an scalar - FALSE\n");
   }
}

Here are some equivalent comparisions using the splice command assuming ($[ == 0 and $#a >= $i )

Add an item on the end of a list push(@a,$x) splice(@a,@a,0,$x)
Remove an item from the end of a list pop(@a)     splice(@a,-1)
Remove an item from the beginning of a list shift(@a) splice(@a,0,1)
Add an item to the beginning of a list unshift(@a,$x,$y) splice(@a,0,0,$x,$y)
set a element array to a value $a[$x] = $y splice(@a,$x,1,$y)

To create a queue you would use push and shift, and to create stack you would use push and pop.

Associative Array Functions

The following functions manipulate associative arrays

keys returns a list of subscripts of the element of an associative array
values returns a list consisting of all the values in an associate array
each returns an associative element as a two element list
delete deletes an associative array element
exists enables you to determine whether a particular element of an associative array exists.
Examples
keys

%array = ("foo", "26", "bar", "27");
@keys = keys(%array);
print("@keys\n");

# keys is commonly used as below
foreach $i (keys (%array)) {
   print $i . "\n";
}

Note: in no particular order will the list be returned
values %array = ("foo", "26", "bar", "27");
@values = values(%array);
print("@values\n");

foreach $i (values (%array)) {
   print $i . "\n";
}

Note: in no particular order will the list be returned
each %array = ("foo", "26", "bar", "27");
@each = each(%array);
print("@each\n");

foreach $i (each (%array)) {
   print $i . "\n";
}

Note: in no particular order will the list be returned, also do not use delete when using each, because the behavior of each unpredictable

delete %array = ("foo", "26", "bar", "27");

$retval = delete($array{"foo"});        # returns the deleted elements value 26

foreach $i (keys (%array)) {
   print $i . "\n";                     # only bar should exist
}

print $retval;         
exists %array = ("foo", "26", "bar", "27");

if ( exists($array{"foo"}) ) {
   print("Foo exists");
} else {
   print ("Foo does NOT exists");
}

When using associative arrays do not use push, pop, shift or splice because the position of any particular element in the array is not guaranteed.