Programming Perl, 4th Edition

log

log EXPR
log

This function returns the natural logarithm (that is, base e) of EXPR. If EXPR is negative, it raises an exception. To get the log of another base, use basic algebra: the base-N log of a number is equal to the natural log of that number divided by the natural log of N. For example:

sub log10 {
    my $n = shift;
    return log($n)/log(10);
}

For the inverse of log, see exp.