opt-file.nf

#!/usr/bin/env nextflow
/*
 * Copyright 2013-2024, Seqera Labs
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

process foo {
  output: 
  path 'missing.txt', optional: true

  '''
  echo miao
  '''
}

process bar {
  input: 
  file x

  '''
  echo bau
  '''
}

workflow {
  foo | bar
}