Control flow

Statement modifiers

Full

Postfix if / unless / for / while — a whole control structure after the statement.

A statement modifier attaches a condition or loop to the end of a single statement — no block, no braces. It reads like English and is the idiomatic form for one-liners.

Postfix if / unless #

say "even" if 4 %% 2;
say "odd" unless 4 %% 2;

Output

even

The unless line produces nothing because 4 %% 2 is true.

Postfix for #

A trailing for runs the statement once per element, with $_ set — so the .method shorthand pairs naturally with it.

say $_ for 1..3;
.say for <a b>;

Output

1
2
3
a
b

Postfix while / until #

my $i = 0;
$i++ while $i < 3;
say $i;

Output

Notes #

Modifiers don't nest and take no else — reach for the block forms (if / unless / with, loops) when you need more than one clause.
The postfix for topicalises $_, exactly like the block for, so .say for @items is the compact "print each" idiom.
Precedence is loose, so the whole statement to the left is the body: say $_ * 2 for 1..3 doubles each element.