Nextflow脚本运行报错：未找到变量result的解决咨询

问题重现 #

刚学习Nextflow，运行参考脚本时出现No such variable: result错误，相关信息如下：

原脚本代码 #

#!/usr/bin/env nextflow  
// Example1 from gist

params.str = 'Hello world!' 

process AFcalc {
    """
    echo  '${params.str}'
    """
}

//this is necessary to print the output
result.subscribe {
    println it.trim()
}

运行命令 #

nextflow run example1.nf 

错误输出 #

N E X T F L O W  ~  version 22.04.5
Launching `example1.nf` [nostalgic_brahmagupta] DSL2 - revision: 17976728a8
No such variable: result
 -- Check script 'example1.nf' at line: 15 or see '.nextflow.log' file for more details

日志详情 #

Oct-02 13:51:35.370 [main] DEBUG nextflow.cli.Launcher - $> nextflow run example1.nf
Oct-02 13:51:35.413 [main] INFO  nextflow.cli.CmdRun - N E X T F L O W  ~  version 22.04.5
Oct-02 13:51:35.446 [main] DEBUG nextflow.cli.CmdRun - Applied DSL=2 by global default
Oct-02 13:51:35.460 [main] INFO  nextflow.cli.CmdRun - Launching `example1.nf` [nostalgic_brahmagupta] DSL2 - revision: 17976728a8
Oct-02 13:51:35.468 [main] DEBUG nextflow.plugin.PluginsFacade - Setting up plugin manager > mode=prod; plugins-dir=/Users/theodosiou/.nextflow/plugins; core-plugins: nf-amazon@1.7.2,nf-azure@0.13.2,nf-console@1.0.3,nf-ga4gh@1.0.3,nf-google@1.1.4,nf-sqldb@0.4.0,nf-tower@1.4.0
Oct-02 13:51:35.469 [main] DEBUG nextflow.plugin.PluginsFacade - Plugins default=[]
Oct-02 13:51:35.474 [main] INFO  org.pf4j.DefaultPluginStatusProvider - Enabled plugins: []
Oct-02 13:51:35.474 [main] INFO  org.pf4j.DefaultPluginStatusProvider - Disabled plugins: []
Oct-02 13:51:35.476 [main] INFO  org.pf4j.DefaultPluginManager - PF4J version 3.4.1 in 'deployment' mode
Oct-02 13:51:35.481 [main] INFO  org.pf4j.AbstractPluginManager - No plugins
Oct-02 13:51:35.511 [main] DEBUG nextflow.Session - Session uuid: ef770a53-e834-4fcd-8ae5-6216009b4ebc
Oct-02 13:51:35.511 [main] DEBUG nextflow.Session - Run name: nostalgic_brahmagupta
Oct-02 13:51:35.512 [main] DEBUG nextflow.Session - Executor pool size: 8
Oct-02 13:51:35.831 [main] DEBUG nextflow.cli.CmdRun - 
  Version: 22.04.5 build 5708
  Created: 15-07-2022 16:09 UTC (18:09 CEST)
  System: Mac OS X 12.6
  Runtime: Groovy 3.0.10 on Java HotSpot(TM) 64-Bit Server VM 17+35-LTS-2724
  Encoding: UTF-8 (UTF-8)
  Process: 50922@LOUKASs-Air [192.168.0.207]
  CPUs: 8 - Mem: 16 GB (90.5 MB) - Swap: 2 GB (356.6 MB)
Oct-02 13:51:35.840 [main] DEBUG nextflow.Session - Work-dir: /Users/theodosiou/Documents/Projects/nextflow/nextflow-example/work [Mac OS X]
Oct-02 13:51:35.840 [main] DEBUG nextflow.Session - Script base path does not exist or is not a directory: /Users/theodosiou/Documents/Projects/nextflow/nextflow-example/bin
Oct-02 13:51:35.846 [main] DEBUG nextflow.executor.ExecutorFactory - Extension executors providers=[]
Oct-02 13:51:35.851 [main] DEBUG nextflow.Session - Observer factory: DefaultObserverFactory
Oct-02 13:51:35.861 [main] DEBUG nextflow.cache.CacheFactory - Using Nextflow cache factory: nextflow.cache.DefaultCacheFactory
Oct-02 13:51:35.867 [main] DEBUG nextflow.util.CustomThreadPool - Creating default thread pool > poolSize: 9; maxThreads: 1000
Oct-02 13:51:35.903 [main] DEBUG nextflow.Session - Session start invoked
Oct-02 13:51:36.227 [main] DEBUG nextflow.script.ScriptRunner - > Launching execution
Oct-02 13:51:36.235 [main] DEBUG nextflow.Session - Session aborted -- Cause: No such property: result for class: Script_0f3fefb4
Oct-02 13:51:36.241 [main] ERROR nextflow.cli.Launcher - @unknown
groovy.lang.MissingPropertyException: No such property: result for class: Script_0f3fefb4
        at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:65)
        at org.codehaus.groovy.runtime.callsite.PogoGetPropertySite.getProperty(PogoGetPropertySite.java:51)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGroovyObjectGetProperty(AbstractCallSite.java:341)
        at Script_0f3fefb4.runScript(Script_0f3fefb4:15)
        at nextflow.script.BaseScript.runDsl2(BaseScript.groovy:170)
        at nextflow.script.BaseScript.run(BaseScript.groovy:217)
        at nextflow.script.ScriptParser.runScript(ScriptParser.groovy:220)
        at nextflow.script.ScriptRunner.run(ScriptRunner.groovy:212)
        at nextflow.script.ScriptRunner.execute(ScriptRunner.groovy:120)
        at nextflow.cli.CmdRun.run(CmdRun.groovy:337)
        at nextflow.cli.Launcher.run(Launcher.groovy:480)
        at nextflow.cli.Launcher.main(Launcher.groovy:639)

问题原因 #

• 原脚本是DSL1写法，但你的Nextflow版本（22.04.5）默认启用DSL2，两者语法差异导致错误。
• DSL1中，流程的输出会自动绑定到与流程同名的变量（如AFcalc流程的输出是AFcalc变量），但脚本中错误使用了未定义的result变量。
• DSL2默认不会自动执行流程，需要通过workflow块显式调用流程并处理输出通道。

修复方案 #

提供两种兼容方案，任选其一即可：

方案1：切换为DSL1模式 #

在脚本开头添加DSL1启用声明，并将订阅对象改为流程名：

#!/usr/bin/env nextflow
nextflow.enable.dsl=1

params.str = 'Hello world!' 

process AFcalc {
    """
    echo  '${params.str}'
    """
}

// 订阅AFcalc流程的输出通道
AFcalc.subscribe {
    println it.trim()
}

方案2：适配DSL2模式 #

使用workflow块执行流程，显式定义输出通道并订阅：

#!/usr/bin/env nextflow

params.str = 'Hello world!' 

process AFcalc {
    // 显式定义输出通道，将标准输出命名为msg
    output:
    stdout emit: msg

    """
    echo  '${params.str}'
    """
}

// 定义工作流，调用流程并处理输出
workflow {
    // 调用AFcalc流程，获取其输出通道
    calc_result = AFcalc()
    // 订阅输出通道中的msg
    calc_result.msg.subscribe {
        println it.trim()
    }
}

验证运行 #

保存修改后的脚本，重新运行命令：

nextflow run example1.nf 

脚本将正常执行，输出Hello world!。

内容的提问来源于stack exchange，提问作者LDT