Question

I’m trying to create a RegEx Validator that checks the file extension in the FileUpload input against a list of allowed extensions (which are user specified). The following is as far as I have got, but I’m struggling with the syntax of the backward slash (\) that appears in the file path. Obviously the below is incorrect because it just escapes the (]) which causes an error. I would be really grateful for any help here. There seems to be a lot of examples out there, but none seem to work when I try them.

[a-zA-Z_-s0-9:\]+(.pdf|.PDF)$

Answer 1

To include a backslash in a character class, you need to use a specific escape sequence (\b):

[a-zA-Z_\s0-9:\b]+(\.pdf|\.PDF)$

Note that this might be a bit confusing, because outside of character classes, \b represents a word boundary. I also assumed, that -s was a typo and should have represented a white space. (otherwise it shouldn’t compile, I think)

EDIT: You also need to escape the dots. Otherwise they will be meta character for any character but line breaks.

another EDIT: If you actually DO want to allow hyphens in filenames, you need to put the hyphen at the end of the character class. Like this:

[a-zA-Z_\s0-9:\b-]+(\.pdf|\.PDF)$