Perl Cookbook

Specifying a List In Your Program

Problem

You want to include a list in your program. This is how you initialize arrays.

Solution

You can write out a comma-separated list of elements:

@a = ("quick", "brown", "fox");

If you have a lot of single-word elements, use the qw() operator:

@a = qw(Why are you teasing me?);

If you have a lot of multi-word elements, use a here document and extract lines:

@lines = (<<"END_OF_HERE_DOC" =~ m/^\s*(.+)/gm);
    The boy stood on the burning deck,
    It was as hot as glass.
END_OF_HERE_DOC

Discussion

The first technique is the most commonly used, often because only small arrays are normally initialized as program literals. Initializing a large array would fill your program with values and make it hard to read, so such arrays are either initialized in a separate library file (see Chapter 12), or the values are simply read from a file:

@bigarray = ();
open(DATA, "< mydatafile")       or die "Couldn't read from datafile: $!\n";
while (<DATA>) {
    chomp;
    push(@bigarray, $_);
}

The second technique uses the qw() operator, one of the quoting operators. Along with q() , qq(), and qx(), qw() provides another way to quote values for your program. q() behaves like single quotes, so these two lines are equivalent:

$banner = 'The Mines of Moria';
$banner = q(The Mines of Moria);

Similarly, qq() behaves like double quotes:

$name   =  "Gandalf";
$banner = "Speak, $name, and enter!";
$banner = qq(Speak, $name, and welcome!);

And qx() is almost exactly like backticks; that is, it ...