You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit 5355a72c746fa5146541d790aece53b22737afee)
sqrt EXPR
sqrt

Return the positive square root of EXPR. If EXPR is omitted, uses $_. Works only for non-negative operands unless you've loaded the Math::Complex module.

use Math::Complex;
print sqrt(-4);    # prints 2i