($chopped) = $s =~ s/^(.)//s;
# or
$s =~ s/^.//s;

##</code><code>##

substr($s, 0, 1) = "";  # no way to get the value back, though...
# Note: you need the parens. Precedence of the assigment is higher than that of the comma.

##</code><code>##

$chopped = substr $s, 0, 1, "";
# or
substr $s, 0, 1, "";