Learning Perl, Second Edition

11.3. Invoking a Format

You invoke a format with the write function. This function takes the name of a filehandle and generates text for that filehandle using the current format for that filehandle. By default, the current format for a filehandle is a format with the same name (so for the STDOUT filehandle, the STDOUT format is used), but we'll soon see that you can change it.

Let's take another look at that address label format, and create a file full of address labels. Here's a program segment:

format ADDRESSLABEL =
===============================
| @<<<<<<<<<<<<<<<<<<<<<<<<<< |
$name
| @<<<<<<<<<<<<<<<<<<<<<<<<<< |
$address
| @<<<<<<<<<<<<<<<<, @< @<<<< |
$city,          $state, $zip
===============================
.

open(ADDRESSLABEL,">labels-to-print") || die "can't create";
open(ADDRESSES,"addresses") || die "cannot open addresses";
while (<ADDRESSES>) {
    chomp; # remove newline
    ($name,$address,$city,$state,$zip) = split(/:/);
        # load up the global variables
    write (ADDRESSLABEL); # send the output
}

Here we see our previous format definition, but now we also have some executable code. First, we open a filehandle onto an output file, which is called labels-to-print. Note that the filehandle name (ADDRESSLABEL) is the same as the name of the format. This is important. Next, we open a filehandle on an address list. The format of the address list is presumed to be something like this:

Stonehenge:4470 SW Hall Suite 107:Beaverton:OR:97005 Fred Flintstone:3737 Hard Rock Lane:Bedrock:OZ:999bc ...