PHP regular expression for given condition [duplicate] - php

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Possible Duplicate:
php regex , extract phone number from text/html
I have following requirement. There is a phone number field.
Its length should be between 8 and 10
It can contain only _ and white spaces
First and last elements should be digits
_ and white spaces should be in between 2 digits
Can I write a regular expression to validate the above things using php?
Example for valid entry: 231_901 347
Example for invalid entry: _123 567, 345__123
Also if possible, can you please write down the preg_match expression.
Here is the code which I tried:
$subject = "_012_345 69";
$pattern = '/[\d]{1}.[\d\s_]{5,10}.[\d]{1}$/';
$matches = preg_match($pattern, $subject);
echo($matches);
It should return 0 but it returns 1.

Answer 1

^(?=.{8,10}$)\d+(?:[ _]\d+)*$
Explanation:
^ # Start of string
(?=.{8,10}$) # Assert length 8-10
\d+ # One or more digits
(?: # followed by
[ _] # one space or underscore
\d+ # one or more digits
)* # zero or more times.
$ # End of string

Answer 2

Use regex pattern
^(?=.{8,10}$)(?=\d)(?=.*\d$)(?:\d|(?<=\d)[\s_](?=\d))+$
Explanation >>
^
Start if line/string
(?=.{8,10}$)
String size is 8-10 characters
(?=\d)
First character is digit
(?=.*\d$)
Last character is digit
(?:\d|(?<=\d)[\s_](?=\d))+
Allowed characters are (a) digits or (b) whitespace or underscore between digits
$
End of line/string

Answer 3

This meets all your requirements as I understand them:
^(?:\d[ _]*){7,9}\d$
As for those false positives you're getting, you just left off the start anchor (^). But even with anchor added it matches things like
1_________2
and
01234567890123
I'm assuming those are invalid because you meant there have to be eight to ten digits, not that the overall length should be eight to ten.