Programming Perl, 4th Edition

Accessing Formatting Internals

For low-level access to the internal formatting mechanism, you may use the built-in formline operator and access $^A (the $ACCUMULATOR variable) directly. (Formats essentially compile into a sequence of calls to formline.) For example:

$str = formline <<'END', 1,2,3;
@<<<  @|||  @>>>
END

say "Wow, I just stored '$^A' in the accumulator!";

Or to create an swrite subroutine that is to write as sprintf is to printf, do this:

use Carp;
sub swrite {
    croak "usage: swrite PICTURE ARGS" unless @_;
    my $format = shift;
    $^A = "";
    formline($format, @_);
    return $^A;
}

$string = swrite(<<'END', 1, 2, 3);
Check me out
@<<<  @|||  @>>>
END
print $string;

If you were using the IO::Handle module, you could use formline as follows to wrap a block of text at column 72:

use IO::Handle;
STDOUT–>formline("^" . ("<" x 72) . "~~\n", $long_text);

Now brace yourself for a big chapter…