How can I format a number to three decimal places with Perl?

Question

I have a number, and need to add a decimal to it for formatting.

The number is guaranteed to be between 999999 and 1000 (I have covered the other possibilities in other ways, this is the one I can't get my head around). I need to put a decimal before the last 3 digits, such as:

999.999 or 1.000 or 23.513

What kind of regex will accomplish this?

Answer 1

$num =~ s/(\d{3})$/.$1/

That says: Take a block of 3 digits (that must be anchored at the END of the string) and replace them with a "." followed by whatever was just matched.

Answer 2

Here is another solution just for the fun of it:

In Perl substr() can be an lvalue which can help in your case.

substr ($num , -3 , 0) = '.';

will add a dot before the last three digits.

You can also use the four arguments version of substr (as pointed in the comments) to get the same effect:

substr( $num, -3, 0, '.' );

I would hope it is more elegant / readable than the regexp solution, but I am sure it will throw off anyone not used to substr() being used as an lvalue.

Answer 3

And yet another way for fun of it ;-)

my $num_3dec = sprintf '%.3f', $num / 1000;

/I3az/

Answer 4

Golf anyone?

substr $num,-3,0,'.';