You are viewing the version of this documentation from Perl blead. This is the main development branch of Perl. (git commit c0b8ab1ec6910f423d6cf550207f108b32af8beb)
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