gohugoio/hugo · error

failed to compile Redirect regexp

Error message

failed to compile Redirect regexp %q: %w

What it means

Emitted by Server.CompileConfig when a redirect's `fromRe` regexp fails to compile via Go's regexp package. This is the regex-based matcher (alternative to glob `from`), used when you need capture groups for substitution in `to`.

Solutions

1. Test `fromRe` with Go regexp semantics (RE2). No backreferences/lookahead.
2. Balance groups; escape metacharacters intended literally.
3. Use named groups or positional groups referenced as $1 in `to`.

Example fix

# before (invalid RE2 lookahead)
[[server.redirects]]
fromRe = "^/old/(?=sub).*"
to = "/new"

# after
[[server.redirects]]
fromRe = "^/old/(.*)"
to = "/new/$1"

python3 - <<'PY'
import tomllib,re
cfg=tomllib.loads(open('hugo.toml').read())
for r in cfg.get('server',{}).get('redirects',[]):
    fr=r.get('fromRe','')
    if fr:
        try: re.compile(fr)
        except re.error as e: print(f"bad fromRe {fr!r}: {e}")
print("redirect regexps ok")
PY

When it happens

Trigger: A `[[server.redirects]]` with `fromRe` set to an invalid Go regexp: unbalanced parens, invalid escape, unsupported syntax.

Common situations: Using PCRE-only syntax unsupported by Go RE2 (e.g. backreferences, lookahead); copy-pasting a regex from another language.

Related errors

• failed to compile Redirect glob
• failed to compile Redirect header glob
• redirects must have either From or FromRe set
• --appendPort=false not supported when in multihost mode
• failed to compile cache buster

AI-assisted analysis of gohugoio/hugo@52c9bd7908 (2026-08-09). Data as JSON: /api/errors/12f45b0e3a35dec2. Report an issue: GitHub.

Appendix: source

Thrown at config/commonConfig.go:277

	}
	for _, r := range s.Redirects {
		if r.From == "" && r.FromRe == "" {
			return fmt.Errorf("redirects must have either From or FromRe set")
		}
		rd := redirect{
			headers: make(map[string]glob.Glob),
		}
		if r.From != "" {
			g, err := glob.Compile(r.From)
			if err != nil {
				return fmt.Errorf("failed to compile Redirect glob %q: %w", r.From, err)
			}
			rd.from = g
		}
		if r.FromRe != "" {
			re, err := regexp.Compile(r.FromRe)
			if err != nil {
				return fmt.Errorf("failed to compile Redirect regexp %q: %w", r.FromRe, err)
			}
			rd.fromRe = re
		}
		for k, v := range r.FromHeaders {
			g, err := glob.Compile(v)
			if err != nil {
				return fmt.Errorf("failed to compile Redirect header glob %q: %w", v, err)
			}
			rd.headers[k] = g
		}
		s.compiledRedirects = append(s.compiledRedirects, rd)
	}

	return nil
}

func (s *Server) MatchHeaders(pattern string) []types.KeyValueStr {
	if s.compiledHeaders == nil {

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