From: Raj (raj.bahad@totalise.co.uk)
Date: Wed Sep 04 2002 - 08:59:15 GMT-3
Hi Group,
I am having problems understanding certain regular expressions. Below, I
have listed two which I think perform the same function, however, the
various examples on cco and Halabi's book still does not clarify the
difference between them.
ip as-path access-list 10 permit ^1 ?[0-9]*$ (from Halabi book)
and
ip as-path access-list 10 permit ^1_[0-9]*$ (from BGP case studies)
I understand that either one of these will permit routes only from directly
connected AS1 and its customers!
What is the difference between the "?" and "_" ?
From what I have read, the "?" means match either a single character or null
value whereas the "_" means match commas, braces, etc...
Unfortunately, even though i have read all the various explanations on this,
I am still confused over the differences between them.
Any help will be appreciated!
Thanks,
Raj.
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