记录一个 Jenkins 中使用 shell 的小问题，纯小白问题
问题
想在 Jenkins 中使用 for 循环来进行 image 推送，但是发现执行失败，报下面错误：
Also: org.jenkinsci.plugins.workflow.actions.ErrorAction$ErrorId: aca6f3b9-ebf2-44dd-b241-2d7dff9d5a78
groovy.lang.MissingPropertyException: No such property: i for class: groovy.lang.Binding
at groovy.lang.Binding.getVariable(Binding.java:63)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onGetProperty(SandboxInterceptor.java:285)
at org.kohsuke.groovy.sandbox.impl.Checker$7.call(Checker.java:375)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:379)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:355)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:355)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:355)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:355)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedGetProperty(Checker.java:355)
at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.getProperty(SandboxInvoker.java:29)
at org.jenkinsci.plugins.workflow.cps.LoggingInvoker.getProperty(LoggingInvoker.java:121)
at com.cloudbees.groovy.cps.impl.PropertyAccessBlock.rawGet(PropertyAccessBlock.java:20)
at WorkflowScript.run(WorkflowScript:325)
at ___cps.transform___(Native Method)
at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.get(PropertyishBlock.java:73)
at com.cloudbees.groovy.cps.LValueBlock$GetAdapter.receive(LValueBlock.java:30)
at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.fixName(PropertyishBlock.java:65)
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
at java.base/java.lang.reflect.Method.invoke(Method.java:580)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.ConstantBlock.eval（ConstantBlock.java:21)
at com.cloudbees.groovy.cps.Next.step(Next.java:83)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:152)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:146)
at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:136)
at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:275)
at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:146)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:187)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:423)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:331)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:295)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:97)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:68)
at jenkins.util.ErrorLoggingExecutorService.lambda$wrap$0(ErrorLoggingExecutorService.java:51)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
at java.base/java.lang.Thread.run(Thread.java:1583)
Finished: FAILURE相应的代码如下：
sh """
docker login -u ${username} -p '${password}' harbor.halfcoffee.com
for i in `cat /home/jenkins/agent/env-images.txt`; do docker push $i ; done
"""解决办法
解法超级简单，在 shell 脚本内，默认 $xx 变量会被 Jenkins 解析成值，这会导致最终运行的脚本内容错误，只需在 $i 前加上 \ 即可让 Jenkins 不进行解析：
sh """
docker login -u ${username} -p '${password}' harbor.halfcoffee.com
for i in `cat /home/jenkins/agent/env-images.txt`; do docker push \$i ; done
"""