rand - retrieve the next pseudorandom number
rand EXPR
rand
Returns a random fractional number greater than or equal to 0 and less than the value of EXPR. (EXPR should be positive.) If EXPR is omitted, the value 1 is used. Automatically calls srand() unless srand() has already been called. See also srand().
(Note: If your rand function consistently returns numbers that are too large or too small, then your version of Perl was probably compiled with the wrong number of RANDBITS.)