In Perl, you can follow any
simple statement with a
single optional modifier -
So, you could write -
$foobar = $foobaz unless $foobaz < 0 ;
if and unless have the expected semantics, foreach will go through each value in EXPR, aliasing $_ to the value and executing the statement. The while and until modifiers have the usual 'while loop' semantics (the conditional is evaluated first) apart from when applied to a do block, in which case the block will execute once before the conditional is evaluated.
This is a pretty cool feature of perl, because it lets you write very "english"-sounding statements. To my mind at least,
statement if conditional;
looks nicer than:
if ( conditional ) { statement; }