How to Workaround Lookarounds in Go Regular Expressions?

Error Parsing Regexp: Invalid or Unsupported Perl Syntax (?!

When attempting to compile a regular expression in Go, users may encounter the following parsing error:

error parsing regexp: invalid or unsupported Perl syntax: (?!

This error is typically raised when trying to use a lookaround operator (?!..., which is not supported in Go's regular expression syntax.

Understanding Lookarounds

Lookarounds are a special type of regular expression operator used to match a pattern only if it is not immediately followed or preceded by another specific pattern. In this case, (?! is being used to check if a given string does not start with the text "On".

Go Regexp Workaround

As Go does not support lookarounds, there are several workarounds available:

Using Separate Regexps

One approach is to use two separate regular expressions:

nonOnRegex := regexp.MustCompile("^(?!On.*On\s.+?wrote:)(On\s(.+?)wrote:)$")
onOnRegex := regexp.MustCompile("^On.*On\s.+?wrote:")

You can then check if the nonOnRegex matches the string and the onOnRegex does not match to determine the desired outcome.

Using Optional Capturing Groups

Another workaround is to use an optional capturing group:

regex := regexp.MustCompile(`^On(.*On)?\s.+?wrote:`)

After matching the string using this regular expression, you can check if the first capturing group exists and ends with "On". If so, return false, otherwise return true.

By implementing one of these workarounds, you can effectively replicate the functionality of lookarounds in Go's regular expression syntax.

The above is the detailed content of How to Workaround Lookarounds in Go Regular Expressions?. For more information, please follow other related articles on the PHP Chinese website!