I'm trying to catch any characters that are not letters, numbers, or .-_ (period, dash, underscore)
My code is
return !preg_match('/[^A-Za-z0-9.-_]/', $strToFilter);
My hope is that it will return false when it find an invalid character. As of now it allows ._ (period and underscore) but does not allow - (dash). It also does not detect characters like /, \, [, ], %, ^, etc as invalid characters.
What is wrong with my expression?
In Regex character classes, you can't match a literal hyphen unless it is:
^), or\)The hyphen can be included right after the opening bracket, or right before the closing bracket, or right after the negating caret. Both [-x] and [x-] match an x or a hyphen. [^-x] and [^x-] match any character thas is not an x or a hyphen. This works in all flavors discussed in this tutorial. Hyphens at other positions in character classes where they can't form a range may be interpreted as literals or as errors. Regex flavors are quite inconsistent about this.
Source - See Metacharacters Inside Character Classes.
Just escape the dash:
return !preg_match('/[^A-Za-z0-9.\-_]/', $strToFilter);
