kestra-io/kestra · error · PebbleException

The argument 'regex' is required.

Error message

The argument 'regex' is required.

What it means

Thrown by the 'regexExtract' Pebble filter when the required `regex` argument is null or absent. The filter declares `regex` (and optional `group`) as named arguments and rejects calls that omit the pattern before attempting compilation.

Source

Thrown at core/src/main/java/io/kestra/core/runners/pebble/filters/RegexExtractFilter.java:57

    private static final String ARGUMENT_REGEX = "regex";
    private static final String ARGUMENT_GROUP = "group";

    private static final List<String> ARGS = List.of(ARGUMENT_REGEX, ARGUMENT_GROUP);

    @Override
    public List<String> getArgumentNames() {
        return ARGS;
    }

    @Override
    public Object apply(Object input, Map<String, Object> args, PebbleTemplate self, EvaluationContext context, int lineNumber) throws PebbleException {
        if (input == null) {
            return null;
        }

        if (args.get(ARGUMENT_REGEX) == null) {
            throw new PebbleException(
                null,
                MessageFormat.format("The argument ''{0}'' is required.", ARGUMENT_REGEX),
                lineNumber,
                self.getName()
            );
        }

        String regex = args.get(ARGUMENT_REGEX).toString();
        int group = args.containsKey(ARGUMENT_GROUP) && args.get(ARGUMENT_GROUP) != null
            ? ((Number) args.get(ARGUMENT_GROUP)).intValue()
            : 0;

        if (group < 0) {
            throw new PebbleException(
                null,
                MessageFormat.format("Group index {0} is out of bounds: must be >= 0.", group),
                lineNumber,
                self.getName()

View on GitHub (pinned to 823fada927)

Solutions

1. Supply the named argument: `{{ s | regexExtract(regex="\\d+") }}`.
2. If regex comes from an input, ensure the input is declared and provided, or default it: `regex=inputs.pattern ?? "\\d+"`.
3. Use raw-string-style escaping consistently (Pebble requires `\\d` for `\d`).

Example fix

# before
{{ "order-12345" | regexExtract }}
# after
{{ "order-12345" | regexExtract(regex="\\d+") }}

# Supply regex, optionally defaulted from an input:
{{ s | regexExtract(regex=inputs.pattern ?? "\\d+") }}

{% if inputs.pattern is not null %}
  {{ s | regexExtract(regex=inputs.pattern) }}
{% endif %}

When it happens

Trigger: Writing `{{ s | regexExtract }}` or `{{ s | regexExtract(group=1) }}` without supplying `regex`; passing a variable for regex that resolved to null (e.g. an unset input).

Common situations: Referencing an undefined input as the pattern: `regexExtract(regex=inputs.missing)`; copy-paste from a regex literal that lost its quotes; refactoring that drops the argument.

Related errors

• Group index {0} is out of bounds: must be >= 0.
• Group index {0} is out of bounds: the pattern has only {1} c
• The argument 'regex' is required.
• The argument ''{0}'' is required.
• The 'jq' filter expects an argument 'expression'.

AI-assisted analysis of kestra-io/kestra@823fada927 (2026-08-14). Data as JSON: /api/errors/852d88243e898ace. Report an issue: GitHub.