You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit bf1aacf4f755a25863a69417c5214aac7693b1c8)
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