Interested to Buy Any Domain ? << Click Here >> for more details...
Write a simple regular expression to match an IP address,
e-mail address, city-state-zipcode combination.
- 15 Answers
- 59231 Views
- I also Faced
- E-Mail Answers
Answer Posted / santosh
The question is not properly framed. A regex is specific to
a language to some extent. Lets frame it more properly and
create some test cases:
1. Writing regex for Perl to identify an IP address.
2. IP address must be a "true" IP address.
3. It must not match anything more than an IP addresses.
4. Must pass the following tests:
a)0.0.0.0: Pass: This is a valid class A address, though a
reserved address. You may not see it often but nevertheless
it is a valid address. See
http://www.lincoln.edu/math/rmyrick/ComputerNetworks/InetRef
erence/26.htm
b)1.1.1.1: Pass
c)255.255.255.255:Pass
d)1.1.1.11111:Fail
e)256.1.1.1:Fail
f)256.256.256.256:Fail
g)-1.-1.-1.-1: Fail
h).... (four dots without any digits in between)
Another test can be presence of extra zeros, which can be
fine or not fine depending upon the OS. For example
01.01.01.01 should or should not be accepted? But we will
ignore it for the time being in our analysis.
Here is an analysis of the solutions given above as well as
my additional solutions:
1. /([0-255])(\.)$1\1$1\1$1/; : This works for egrep and
possibly vi and other *nix tools such as emacs. This does
*not* work for Perl because [0-255] will match
digits '0','1', '2' and '5' only. It will not match 63.
2. /((\d{1,3})(\.)){3}\d{1,3}/: Written for Perl as
obviously {} syntax is not available for many other
scripting languages. This does not check the semantics of
IP addresses. Fails tests d, e, f above.
3. (/(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/ && $1 <
255 && $2 < 255 && $3 < 255 && $4 < 255 ): Is almost
correct. Only fails d in above tests. However, it uses
logical expressions and is not a pure regular expression.
Checking for word boundaries will correct it. For example,
(/\b(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\b/ && $1 <
255 && $2 < 255 && $3 < 255 && $4 < 255 ) will pass d
above.
4. r'\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}
(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b': Passes all the
tests. This is the best answer.
5. /^([1-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.([0-9]|[1-9]
\d|1\d\d|2[0-4]\d|25[0-5])\.([0-9]|[1-9]\d|1\d\d|2[0-4]\d|25
[0-5])\.([0-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])$/: Fails
test a. But only because it was meant to eliminate 0.0.0.0.
Otherwise this is okay, though a little verbose. #4 above
can be modified slightly to take care of 0.0.0.0 case and
is less verbose.
Hope this helps.
Regards,
Santosh
| Is This Answer Correct ? | 7 Yes | 1 No |
Post New Answer View All Answers
What does undef function in perl?
What is the closure in PERL?
Write a program to download the contents from www.perlinterview.com/answers.php website in Perl.
How do find the length of an array?
Write the program to process a list of numbers.
How to open a directory in perl?
You want to print the contents of an entire array. How would you do that?
Explain the meaning of closure in perl.
How to convert arrays into a string in perl?
Explain subroutine in perl?
Distinguish my and local?
What is Perl?
What is the purpose of redo statement?
What are the advantages of c over Perl?
What is grep used for in perl?
