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regexregex-negationmessage-passing

Can I make a regex match all characters up to ; except \;?

I am going to construct a message-passing system whose messages have the following structure:

message type;message content

(matches message type;)

However, the user can set the message type, and (for the sake of loosely coupled systems) I want to allow them to use a ; as part of the message type. To do this, I'll have the message constructor escape it with a \:

tl\;dr;Too long; didn't read content

(matches tl\;dr;)

How can I have a regex match all content up to the first ; that's not \;? In the example, that's the tl\;dr; part only. Note that there can be an unescaped ; within the message content.

I tried ^.*;, but that matches all content up to a semicolon within the message (e.g. tl\;dr;Too long;)

Solution 
  • /.*?[^\\](?=;)/

    You could also just use ; instead of (?=;), but the latter prevents it from being part of the full match.

    If you only want to match from the start of the string, use:

    /^.*?[^\\](?=;)/