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Write a simple  regular expression to match an IP address, 
e-mail address, city-state-zipcode combination. 
 Question Submitted By :: CGI-Perl
I also faced this Question!!     Answer Posted By  
# 1
(/(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/ && $1 < 255 &&
$2 < 255 && $3 < 255 && $4 < 255 )
Is This Answer Correct ?    18 Yes 4 No
Abhishek Sagar
# 2
ip_pattern = 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' 
Is This Answer Correct ?    16 Yes 5 No
# 3

Is This Answer Correct ?    25 Yes 18 No
# 4
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) 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
b) Pass
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 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

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]
[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
Otherwise this is okay, though a little verbose. #4 above
can be modified slightly to take care of case and
is less verbose.

Hope this helps.

Is This Answer Correct ?    6 Yes 1 No
# 5
sub validate_ip {

my $ip = shift;

if ( $ip =~ m/^([1-9]|1[0-9]{1,2}|2[0-4]\d|25[0-5])(\.([0-9]|1[0-9]{1,2}|2[0-4]\d|25[0-5])){3}$/ ) {
return 0;
} else {
return 1;

Is This Answer Correct ?    4 Yes 3 No
# 6
Below Solution is applicable IP only :

(/(\d{1,})\.(\d{1,})\.(\d{1,})\.(\d{1,})/ && $1<256 &&
$2<256 && $3<256 && $4<256)
Is This Answer Correct ?    1 Yes 0 No
# 7
Hi all,
Here is the regular expression for matching the valid ip

Let me know your comments.

Is This Answer Correct ?    0 Yes 0 No
# 8
All those above answer are wrong...because all of them take as valid IP address which is not the case...with
computer science ...

Developed By Anshuman sengupta

Reviewed by Arnab Bose

Tested by Avishek chatterjee

-- WHAT DORKS ! and Its tested, No wonder we need
versions/upgrades !
Is This Answer Correct ?    0 Yes 0 No
# 9

print $ip;

This will match for all ip address
Is This Answer Correct ?    0 Yes 0 No
# 10
Is This Answer Correct ?    0 Yes 0 No

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