Of course, once we have created a list array, we can do
much more than just access the elements. We can also
manipulate the elements in many ways. In CGI,
list arrays are most often manipulated using the
operators push, pop, shift and unshift.
Push is used to add a new element on the right hand side
of a list array. Thus, the following code would create a
list array of ("red", "green", "blue")
@colors = ("red", "green");
push (@colors, "blue");
In other words, the push operator, adds an element to
the end of an existing list.
Pop does the exact same thing as push, but in reverse.
Pop extracts the right side element of a list array using the
following syntax:
$popped_value = pop (@array_name);
Thus, we might pop out the value blue from @colors
with the following syntax:
$last_color_in_list = pop (@colors);
Thus, the @colors array now contains only "red" and
"green" and the variable $last_color_in_list is equal to
"blue".
Unshift does the exact same thing as push, but it
performs the addition to the left side of the list array
instead of to the right. Thus, we would create the list
("blue", "red", "green") with the following syntax:
@colors = ("red", "green");
unshift (@colors, "blue");
Similarly, shift works the same as pop, but to the left side
of the list array. Thus, we reduce @colors to just "red"
and "green" by shifting the first element blue with the
following syntax:
$first_color_in_list = shift(@colors);
Thus, @colors again contains only "red" and "green" and
$first_color_in_list equals blue.
Though push, pop, shift, and unshift are the most
common list array manipulation functions used,
there are many others covered in more complete
references. The following table summarizes some of the common
array manipulating operators.
