Fix

The error "invalid or unsupported Perl syntax" occurs because Go's regexp package uses RE2 syntax, which does not support Perl-specific features like lookaheads or backreferences. Replace the unsupported Perl syntax with standard RE2-compatible patterns. For example, change (?=...) (lookahead) to a simpler pattern or use strings.Contains for logic that requires lookahead.

// Incorrect: Perl lookahead syntax
re := regexp.MustCompile(`(?=.*[A-Z])(?=.*[a-z])`) // Error: invalid syntax

// Correct: Use multiple checks or simpler patterns
hasUpper := regexp.MustCompile(`[A-Z]`) 
hasLower := regexp.MustCompile(`[a-z]`) 
if hasUpper.MatchString(s) && hasLower.MatchString(s) {
    // Valid
}

Go uses a different set of rules for regular expressions than Perl. If you copy a pattern directly from Perl, it might use features Go doesn't understand, causing this error. You need to rewrite the pattern using only the features Go supports, often by breaking complex logic into simpler checks.