too many '<' for heredoc on line #%d; only use two, for exam

Error message

too many '<' for heredoc on line #%d; only use two, for example <<END

What it means

The heredoc opener used three or more '<' characters (e.g. <<<EOF). Caddy heredocs use exactly two: <<MARKER. Three-angle heredocs are a bash-ism ('here-string') that Caddy does not support.

Source

Thrown at caddyconfig/caddyfile/lexer.go:163

			}

			// skip CR, we only care about LF
			if ch == '\r' {
				continue
			}

			// after hitting a newline, we know that the heredoc marker
			// is the characters after the two << and the newline.
			// we reset the val because the heredoc is syntax we don't
			// want to keep.
			if ch == '\n' {
				if len(val) == 2 {
					return false, fmt.Errorf("missing opening heredoc marker on line #%d; must contain only alphanumeric characters, dashes and underscores; got empty string", l.line)
				}

				// check if there's too many <
				if string(val[:3]) == "<<<" {
					return false, fmt.Errorf("too many '<' for heredoc on line #%d; only use two, for example <<END", l.line)
				}

				heredocMarker = string(val[2:])
				if !heredocMarkerRegexp.Match([]byte(heredocMarker)) {
					return false, fmt.Errorf("heredoc marker on line #%d must contain only alphanumeric characters, dashes and underscores; got '%s'", l.line, heredocMarker)
				}

				inHeredoc = true
				l.skippedLines++
				val = nil
				continue
			}
			val = append(val, ch)
			continue
		}

		// if we're in a heredoc, all characters are read as-is
		if inHeredoc {

View on GitHub (pinned to 50e54ee279)

Solutions

Change <<<MARKER to <<MARKER
If a here-string was intended, inline the value directly as a normal argument instead

Example fix

# before
respond <<<EOF
# after
respond <<EOF

Defensive patterns

Strategy: validation

Validate before calling

if strings.Contains(line, "<<<") {
    return fmt.Errorf("three-angle heredoc not supported: %q", line)
}

Prevention

Use exactly two '<' for heredocs
Don't paste shell here-strings into Caddyfiles

When it happens

Trigger: A Caddyfile line contains '<<<' before the marker on the opening heredoc line; the lexer detects val[:3] == "<<<" when the newline arrives.

Common situations: Copy-pasting shell scripts or examples that use <<< into a Caddyfile directive, or muscle memory from bash here-strings.

Related errors

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/60e908f6c94d9c1f. Report an issue: GitHub.