Reg Ex for a File name

Question

4.00/5 (1 vote)

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Allowed characters

1. a-z
2. A-Z
3. -(minus)
4. .(dot) should come in the middle of the string and only once
5. (space)

What I am doing is
^[a-zA-Z0-9'- ]+[\.]?[a-zA-Z0-9'- ]+$

it dosent work. JS error - Invalid range in character set

I even tried escaping the minus still same error

^[a-zA-Z0-9'\- ]+[\.]?[a-zA-Z0-9'\- ]+$

please help

Posted 19-Dec-13 1:17am

maverick12131

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Brian A Stephens · Answer 1 · 2013-12-19T02:34:00

Solution 2

The error you are getting is because a literal dash in a character set must be first or last. Otherwise it is interpreted as indicating a range:
^[-a-zA-Z0-9' ]+[\.]?[-a-zA-Z0-9' ]+$

I'm assuming you have these more restrictive rules for your filenames for a reason. Other characters are allowed in filenames, and there are standard regexes out there. Even so, I have some comments about your regex in case it's not what you intended:

- You state that there should always be a dot, but your regex doesn't require it. Again, for standard file naming, an extension is not required, so that's OK.

- To match the dot, your [\.]? is overkill. The literal dot needs to be escaped (\.?) or put in a character class ([.]?), but not both.

- Because of the way you've split the character classes with the possible dot in the middle, your regex requires the filename to be at least two characters (at least one matching before the dot, at least one after). If you are trying to have an optional extension, this would be a better representation of the meaning, and allow single-character filenames:
^[-a-zA-Z0-9' ]+(\.[-a-zA-Z0-9' ]+)?$

Posted 19-Dec-13 2:34am

Brian A Stephens

Updated 19-Dec-13 4:22am

v4

Comments

maverick12131 20-Dec-13 2:19am

its not a mandate to have the dot always.
its just that the dot should be persent only 1 time (zero or one occourance)

also the reg ex you mentioned is not accepting any dots. Not even 1
^[-a-zA-Z0-9' ]+(\.[-a-zA-Z0-9' ]+)?$

Brian A Stephens 20-Dec-13 8:21am

OK, so my regex is what you need. It allows for the possibility of one dot followed by more letters or numbers. I'm not sure why you're not getting it to work. Can you post your code? If you are using
new RegExp(" ... ")
syntax, be sure you escape the escape character (double backslash) because it's also an escape character within quotes.

maverick12131 21-Dec-13 1:05am

Brian A Stephens 30-Dec-13 9:40am

The code tells it all! You are trying to validate each character on its own, but your requirements make this impossible ("dot should come in the middle of the string and only once"). Because of the dot validation, you must consider the entire string, not just one letter. You will need to change this line:
var str = $('#txtFileName').val();

But you still have the problem that keypress happens BEFORE the new text becomes part of the input field value. You need to validate the text that includes the new key. That can only happen in keyup, but that's too late to prevent the key's action.

You need to either validate the entire filename on submit rather than entry, or keep track of a "previous" value for the input so you can revert it back in a keyup handler if the new value doesn't validate.

Member 10434230 · Answer 2 · 2013-12-19T01:24:00

Solution 1

var filename = 'FileName'; // enter your file name here
alert(filename.match(/^\s*[a-z-._\d,\s]+\s*$/i))

Posted 19-Dec-13 1:24am

Member 10434230