More regular expression woes

>I've tried this:
>
>\d{7,8}
>
>but that allows 123456789 to pass, presumably because it contains a string
>of seven or eight digits...

>Hi,
>
>This time, I'm looking for a regular expression which says "the
>string must contain exactly seven or exactly eight digits" e.g.
>
>123456 fails
>1234567 passes
>12345678 passes
>123456789 fails
>
>I've tried this:
>
>\d{7,8}
>
>but that allows 123456789 to pass, presumably because it contains a
>string of seven or eight digits...
>
>Is there any way to specifiy a fixed length to validate?
>
>Any assistance gratefully received.
>
>Mark

Right. To do what you want you'll have to use a delimiter surrounding the
expression. ^ (start of line) and $ (end of line) could do, like this:
>
^\d{7,8}$

Of course, if you have strings that contain nothing but that number you're
looking at, it may be considerably more performant to look at the length
of the string combined with a simpler check that the characters are all
digits (leaving out regular expressions entirely).

Another delimiter that could be useful to you would be \b, which denotes a
"word boundary". For the exact definition you'd best look at the regular
expression docs on MSDN.

Yet another idea could be to delimit by characters that are not digits -
this makes sense and can be very helpful in more complex situations. Like
this:
>
[^\d]\d{7,8}[^\d]

>Of course you're right about that. I'm finally (and I mean after nearly 20
>years of programming!) trying to actually learn regular expressions
>properly...

>I'm using this: http://www.ultrapico.com/Expresso.htm which seems about
>the best I've seen so far...

Hello Mark,
>>
A very good idea, if you ask me :-) Of course, learning the right
situations where to use them is just as important :-) I think the
context of your use case is probably very important to make that decision.
>>
There's also Regulator (http://sourceforge.net/projects/regulator/)
which is very good (better than Expresso IMO), but I've had pretty bad
problems in the past with the editor component used in that program and
the author Roy Osherove hasn't been responsive at all when I sent him
bug reports.
>
>
Oliver Sturm

>I like Regulator too. Didn't have issues so far (but I don't use it very
>intensively).

>From: "Brad Prendergast" <format('bradp%sbpsoftware.com',['@'])>
>Subject: Re: More regular expression woes
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>Mark Rae <mark@markNOSPAMrae.comwrote in message
><ud4wgxvQHHA.4744@TK2MSFTNGP02.phx.gbl>:
>>
Regex r;
r = new Regex("^\\d{7,8}$");
>
>--
>Brad Prendergast
>"There's a fine line between genius and insanity. I have erased this
>line." -- Oscar Levant (1906 - 1972)
>

@"\b\d{7}\b|\b\d{8}\b",

>From: "Oliver Sturm" <oliver@sturmnet.org>
>Subject: Re: More regular expression woes
>References: <ud4wgxvQHHA.4744@TK2MSFTNGP02.phx.gbl>

>Date: Tue, 30 Jan 2007 19:39:36 +0000
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>Hello John,
>>
>An interesting additional idea, although obviously not really flexible - I
>would opt for the flexibility of \d{7,8} as long as I can make it work.
>Furthermore, your example could be less confusing, IMO, as
>
\b(\d{7}|\d{8})\b
>
>Or of course, as
>
\b\d{7,8}\b
>
>which brings us back to what has already been mentioned. Maybe I'm missing
>the point of your post?
>
>
Oliver Sturm
>--
>http://www.sturmnet.org/blog
>