use Regexp::Common;
    /^\s*$RE{num}{real}\s*[a-z]{1,2}\s*$/;
[download]

Abigail

   s/(\D+)$//;
   my $units = $1;
[download]

Then proceed with the more standard problem of recognizing a number. See:

• How do I determine whether a scalar is a number/whole/integer/float?
• Checking whether a $var is a number

Normalizing your input in this way can be a powerful trick that allows you to more clearly identify and deal with your edge cases. Unless performance is absolutely stupendously crucial there is no reason to implement a monolithic regexp that handles every possibility.

Matt

/^([+-]?(?=\d|\.\d)\d*\.?\d*)([a-z]+)$/
[download]

/^([+-]?(?:\d+\.?\d*|\.\d+))([a-z]+)$/
[download]

I think the following regex should meet these conditions:
/(\-?(?:\d+(?:\.\d+)?)|(?:\.\d+))([a-z]{1,2})/g

The issue that makes this ones non-trivial is that the decimal point and digits are either a required element or an optional element depending on the presence of a whole number.

My regex should return a list containing value/unit pairs... If you want to exactly match and retreive you should use:
/^([+\-]?(?:\d+(?:\.\d+)?)|(?:\.\d+))([a-z]{1,2})$/

That is either a two-element list with the value and the unit, or an empty list.

I think this regex will also give false positives, because it would now also match something like '+cm'.

There is no way around the '|' I think, because the decimal part is what you might call optionally optional; it is only optional if there is a whole part of the number. Because of this, you can't always use the ? modifier to make the decimal part optional.

The only other ways I could think of would use experimental regex features. Even zero-width look-behind or look-ahead assertions can't be aplied here I think...

But I've finally been referenced by name on Perlmonks! Made my day!

:)

Though I was dumb enough to actually post will not being logged in... There go my votes... ;)

Ah, yes, you are absolutely correct, I overlooked the fact that doing:

(\d*(?:\.\d+)?)

Would allow both the whole number and the decimal portions to match 'nothing at all' as I so aptly described in my breakdown.

One more case of testing too many things that should work and not enough things that shouldn't.

Long ago I came up with Extract numbers as a very simple method for pulling numbers out of text that works in lots of cases.

This thread made me realize that I could make it even simpler while making it more effective. I've updated it to reflect this.

The code now reads: my @numbers= $text =~ /([-+\d.eE]+\d)/g; so you could apply this principle to your situation with my( $number, $units )= $text =~ /([-+\d.eE]+\d)(.*)/; It isn't a perfect solution but I think it is worth considering just for its extreme simplicity.