Полезная информация

Learning Perl on Win32 Systems

Learning Perl on Win32 SystemsSearch this book
Previous: 3.6 <STDIN> as an ArrayChapter 3
Arrays and List Data
Next: 3.8 Exercises
 

3.7 Variable Interpolation of Arrays

Like scalars, array values may be interpolated into a double-quoted string. A single element of an array will be replaced by its value, like so:

@fred = ("hello","dolly");
$y = 2;
$x = "This is $fred[1]'s place";    # "This is dolly's place"
$x = "This is $fred[$y-1]'s place"; # same thing

Note that the index expression is evaluated as an ordinary expression, as if it were outside a string. It is not variable interpolated first.

If you want to follow a simple scalar variable reference with a literal left square bracket, you need to delimit the square bracket so it isn't considered part of the array, as follows:

@fred = ("hello","dolly");  # give value to @fred for testing
$fred = "right";
# we are trying to say "this is right[1]"
$x = "this is $fred[1]";    # wrong, gives "this is dolly"
$x = "this is ${fred}[1]";  # right (protected by braces)
$x = "this is $fred"."[1]"; # right (different string)
$x = "this is $fred\[1]";   # right (backslash hides it)

Similarly, a list of values from an array variable can be interpolated. The simplest interpolation is an entire array, indicated by giving the array name (including its leading @ character). In this case, the elements are interpolated in sequence with a space character between them, as in:

@fred = ("a","bb","ccc",1,2,3);
$all = "Now for @fred here!";
            # $all gets "Now for a bb ccc 1 2 3 here!"

You can also select a portion of an array with a slice:

@fred = ("a","bb","ccc",1,2,3);
$all = "Now for @fred[2,3] here!";
            # $all gets "Now for ccc 1 here!"
$all = "Now for @fred[@fred[4,5]] here!"; # same thing

Once again, you can use any of the quoting mechanisms described earlier if you want to follow an array name reference with a literal left bracket rather than an indexing expression.


Previous: 3.6 <STDIN> as an ArrayLearning Perl on Win32 SystemsNext: 3.8 Exercises
3.6 <STDIN> as an ArrayBook Index3.8 Exercises