You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit 0a05a8bd231063e1ba6d039754d9e635d47441b5)
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