RegEx for matching “A-Z, a-z, 0-9, _” and “.”

Question

I need a regex which will allow only A-Z, a-z, 0-9, the _ character, and dot (.) in the input.

I tried:

[A-Za-z0-9_.] 

But, it did not

Answer 1

Working from what you've given I'll assume you want to check that someone has NOT entered any letters other than the ones you've listed. For that to work you want to search for any characters other than those listed:

[^A-Za-z0-9_.]

And use that in a match in your code, something like:

if ( /[^A-Za-z0-9_.]/.match( your_input_string ) ) {
   alert( "you have entered invalid data" );
}

Hows that?

Answer 2

^[A-Za-z0-9_.]+$

From beginning until the end of the string, match one or more of these characters.

Edit:

Note that ^ and $ match the beginning and the end of a line. When multiline is enabled, this can mean that one line matches, but not the complete string.

Use \A for the beginning of the string, and \z for the end.

See for example: http://msdn.microsoft.com/en-us/library/h5181w5w(v=vs.110).aspx

Answer 3

You could simply use ^[\w.]+ to match A-Z, a-z, 0-9 and _

Answer 4

Maybe, you need to specify more exactly what didn't work and in what environment you are.

As to the claim that the dot is special in a charackter class, this is not true in every programming environment. For example the following perl script

use warnings;
use strict;

my $str = '!!!.###';
$str =~ s/[A-Za-z_.]/X/g;
print "$str\n";

produces

!!!X###

Answer 5

regex: /^[a-zA-Z0-9_.]$/i

This works