Perl in a Nutshell, 2nd Edition

while loops

The while statement repeatedly executes a block as long as its conditional expression is true. For example:

while (<INFILE>) {
    chomp;
    print OUTFILE, "$_\n";
}

This loop reads each line from the file opened with the filehandle INFILE and prints them to the OUTFILE filehandle. The loop will cease when it encounters an end-of-file.

If the word while is replaced by the word until, the sense of the test is reversed. The conditional is still tested before the first iteration, though.

The while statement has an optional extra block on the end called a continue block. This block is executed before every successive iteration of the loop, even if the main while block is exited early by the loop control command next. However, the continue block is not executed if the main block is exited by a last statement. The continue block is always executed before the conditional is reevaluated.