$s = "a=1, b=2, c=3";
$s =~ s/a=(\d+), b=(\d+), c=(\d+)/a=$2, b=$3, c=$1/;

##</code><code>##

@n{a, b, c} = (1, 2, 3);
@n{a, b, c} = @n{b, c, a};