You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit bb3b5a6b4200a22651478e4804c30dcb289d6c3f)
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