Regular Expression Question

[mwmarkland]

I have been reading _The Ruby Way_ and am confused by the temperature
conversion sample program on page 14.

The line in question is

abort "#{temp} is not a valid number." if temp !~ /-?\d+/

What I do not understand is that if \d matches "digits", which I
understand to be [0-9], how can this expression match "98.6", which it
seems to do just fine.

Thank you in advance for the clarification.

(I have the 2nd Edition of _The Ruby Way_, First Printing. I have run
the example using ruby 1.8.5 (2007-03-13 patchlevel 35) [i386-linux]).

Matt

 

[Bill Kelly]

I have been reading _The Ruby Way_ and am confused by the temperature
conversion sample program on page 14.

The line in question is

abort "#{temp} is not a valid number." if temp !~ /-?\d+/

What I do not understand is that if \d matches "digits", which I
understand to be [0-9], how can this expression match "98.6", which it
seems to do just fine.

Hi,

Since that regexp isn't anchored, it only cares whether a digit
appears anywhere in the string.

It would be happy with "abc1def".

If you anchor it, like: /\A-?\d+\z/

Then it will require an exact match, caring about all characters
between the beginning and end of the string.


Hope this helps,

Bill

 

[Robert Dober]

I have been reading _The Ruby Way_ and am confused by the temperature
conversion sample program on page 14.

The line in question is

abort "#{temp} is not a valid number." if temp !~ /-?\d+/

What I do not understand is that if \d matches "digits", which I
understand to be [0-9], how can this expression match "98.6", which it
seems to do just fine.

Thank you in advance for the clarification.

Well I guess you are a bright student.
The regexp part has been nicely answered by Bill and it follows that a
regular expression allowing for all kind of different string
representations of Floats is quite
complex.
Why not let ruby do the work for us
May I introduce you to this idiom:

Float( temp ) rescue abort temp << " is not a valid number."

Cheers
Robert

(I have the 2nd Edition of _The Ruby Way_, First Printing. I have run
the example using ruby 1.8.5 (2007-03-13 patchlevel 35) [i386-linux]).

Matt