What is the pattern match for a string which can allow Alpha numeric, underscore and dot

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Hi,

I have a specific requirement where a string should be verified whether it contains only the below:
1. Alphabets (smaller and upper cases)
2. Numbers
3. Dot .
4. Underscore _

The string can have any combination of the above 4 but not other than these.

Thanks & Regards,
Mathi

Posted 21-Jan-15 0:29am

Mathi2code

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5 solutions

Solution 2

This is one expression that should do the trick

^[a-zA-Z1-9_\.]+$

a-zA-Z Will get lower and upper case English characters
1-9 Will get numbers
\. Will get the dot
_ Will get the underscore

There are many other ways to do this.
Have a look at Regular Expressions Info/[^]

Posted 21-Jan-15 0:41am

George Jonsson

Comments

Mathi2code 21-Jan-15 6:46am

I think the escape sequence is not required for dot.

George Jonsson 21-Jan-15 7:14am

It is. A dot without escape sequence will grab any character.
"The dot matches a single character, without caring what that character is. The only exception are line break characters. In all regex flavors discussed in this tutorial, the dot does not match line breaks by default."
See http://www.regular-expressions.info/dot.html[^]

jaket-cp 21-Jan-15 7:32am

0-9 :)
agreed on the dot escape

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Peter Leow · Accepted Answer · 2015-01-21T00:41:00

Solution 3

Try this:

^[\d\._\w]+$

also read: The 30 Minute Regex Tutorial[^]

Posted 21-Jan-15 0:41am

Peter Leow

Comments

Mathi2code 21-Jan-15 6:48am

I tried using this but got unrecognised escape sequence as build error. If I remove that escape sequence it didnt work as expected.

Peter Leow 21-Jan-15 6:52am

put it into string literal for use in c# programs like this:
@"^[\d\._\w]+$"
test it here: http://derekslager.com/blog/posts/2007/09/a-better-dotnet-regular-expression-tester.ashx

Mathi2code 21-Jan-15 8:42am

this worked thanks

Staffan Bruun · Accepted Answer · 2015-01-21T00:49:00

Solution 4

I assume you mean ASCII letters only. In that case, this should do the trick:

C#

Regex regex = new Regex("^[0-9a-zA-Z._]+$");

if(regex.IsMatch(stringToTest))
{
    // string is OK.
}
else
{
    // string is not OK.
}

Posted 21-Jan-15 0:49am

Staffan Bruun

Comments

George Jonsson 21-Jan-15 7:16am

The dot (.) should be escaped.

Staffan Bruun 21-Jan-15 7:25am

Not when it is part of a character class.

Mathi2code · Accepted Answer · 2015-01-21T00:50:00

Solution 5

C#

Regex checkString = new Regex("^[0-9a-zA-Z._]+$");

Even this works with ^ in the start and + with the $

Thanks & Regards,
Mathi.

Posted 21-Jan-15 0:50am

Mathi2code

Comments

George Jonsson 21-Jan-15 7:21am

The dot (.) should be escaped

Mathi2code · Accepted Answer · 2015-01-21T00:39:00

Solution 1

C#

Regex checkString = new Regex("[0-9a-zA-Z._]$");

Posted 21-Jan-15 0:39am

Mathi2code