How to validate file name and file extension from single Regex?

Question

I'm trying to validate my file name and file extension using regular expression. My file name should only contain these characters:'A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,0,1,2,3,4,5,6,7,8,9,_,.,@,-,(,), ' and my extension only should accept .txt files. My current function is pretty complicated and requires nested looping what I don't like. So I would like to check all of this in one single expression. Here is my current code:

fileName = 'My Document.txt'
fileExt = fileName.substr(fileName.length-4)
validCharList='A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z,0,1,2,3,4,5,6,7,8,9,_,.,@,-,(,), ';
err = false;
letterOk = false;

    for(i=0;i<fileName.length;i++){
        letterOk = false;
        for(b=0;b<validCharList.length;b++){
            if(fileName.charAt(i) == validCharList.charAt(b)){
                letterOk = true;
                break;
            }   
        }

       if(letterOk == false){
            alert('file name has an invalid character.');
            return false;
            break;
       }
    }

if(fileExt != '.txt' && fileExt != '.TXT'){
     alert("Your document does not have a proper file extension.")
     return false;
}

If anyone can help with this please let me know. Thanks!

David Hedlund · Accepted Answer · 2016-10-04 14:05:10Z

8

Something like this?

return /^[a-z0-9_.@()-]+\.txt$/i.test(fileName);

If you want two separate checks, are you indicate in comments, you might do something like this:

var validFilename = /^[a-z0-9_.@()-]+\.[^.]+$/i.test(fileName);
var validExtension = /\.txt$/i.test(fileName);

The first expression tests everything up until the last period, and verifies that there is at least one non-period character after the last period, comprising the extension.

If you don't want to bother with the definition of what is a filename, you may instead invert the test, and explicitly check for the presence of invalid characters (here I'm testing the entire string again, so validFilename will be false even if you have invalid characters only in the extension - one way around that would be to validate extension before filename)

var validFilename = !/[^a-z0-9_.@()-]/i.test(fileName);

edited Oct 4, 2016 at 14:05

answered Oct 3, 2016 at 20:40

David Hedlund

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15 Comments

espresso_coffee Over a year ago

Thanks! Regular expression above should cover upper/lower case too?

Wiktor Stribiżew Over a year ago

The ^[a-z0-9_.@-()]+\.txt$ regex is incorrect.

espresso_coffee Over a year ago

@WiktorStribiżew how correct expression looks like?

Wiktor Stribiżew Over a year ago

If you add more chars to the regex above, do not forget to keep hyphen at the end of the character class. Or add \ before it.

David Hedlund Over a year ago

@espresso_coffee: Your extension test looks alright, but don't forget the /i, to ignore case. For the filename, you've forgotten the +, meaning it'll look for only a single character, and not a set of many characters matching the pattern. Another issue is that since you're losing the $, you're not testing the full string. Even with the +, you'd only be validating that the name starts with valid characters, not that it contains only valid characters. See my edited answer for a possible solution.

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Pallav Chanana · Accepted Answer · 2019-09-03 06:48:29Z

0

Try this for single line check of filename and extension using single regex.

 const validFilename = /^[\w,\s-]+\.[A-Za-z0-9]{3}$/i.test('filename');

answered Sep 3, 2019 at 6:48

Pallav Chanana

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