Regex-How to prevent repeated special characters?

I don't have an experience on Regular Expressions. I need to a regular expression which doesn't allow to repeat of special characters (+-*/& etc.) The string can contain digits, alphanumerics, and special characters.

This should be valid : abc,df

This should be invalid : abc-,df

i will be really appreciated if you can help me ! Thanks for advance.

Two solutions presented so far match a string that is not allowed.

But the tilte is How to prevent..., so I assume that the regex should match the allowed string. It means that the regex should:

• match the whole string if it does not contain 2 consecutive special characters,
• not match otherwise.

You can achieve this putting together the following parts:

• ^ - start of string anchor,
• (?!.*[...]{2}) - a negative lookahead for 2 consecutive special characters (marked here as ...), in any place,
• a regex matching the whole (non-empty) string,
• $ - end of string anchor.

So the whole regex should be:

^(?!.*[!@#$%^&*()\-_+={}[\]|\\;:'",<.>\/?]{2}).+$

Note that within a char class (between [ and ]) a backslash escaping the following char should be placed before - (if in the middle of the sequence), closing square bracket, a backslash itself and / (regex terminator).

Or if you want to apply the regex to individual words (not the whole string), then the regex should be:

\b(?!\S*[!@#$%^&*()\-_+={}[\]|\\;:'",<.>\/?]{2})\S+