Why Doesn\'t My Regex Negated Set Work in Go?

Regex Negated Set Not Working in Go

A user has encountered an issue where their regular expression behaves differently in Go compared to online regex parsers. The aim is to match file names with specific conditions, excluding those with certain file extensions. However, using a negated set (?!) in the expression doesn't produce the desired results in Go.

Go's RE2 Engine and Lack of Lookaround Support

The Go standard library employs the RE2 engine, which lacks support for certain features, including lookahead operators (?!). This means the negated lookahead operator used in the user's expression is not supported in Go.

Alternative Solution Using Simplified Expression

To achieve the intended functionality, the user can simplify the expression to match the desired characteristics of the filename. Instead of using a negated set, a more explicit pattern can be employed, such as .w{3}$:

• . represents a literal period.
• w{3} specifies three consecutive word characters (letters, numbers, or underscores).
• $ indicates the end of the string.

This simplified expression ensures that the file name ends with a three-character file extension without the need for a negated set.

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