title: Executing shell command in groovy throws 'unexpected char' error
body: <p>I am trying to execute a shell command n groovy</p>
  
  <pre><code>def shellString = "s/\[\|]\|\s\|'\|(\|)//g"
  def temp2 = "echo response| sed -e ${shellString}".execute()
  </code></pre>
  
  <p>It throws compilation error:</p>
  
  <pre><code>org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
  WorkflowScript: 33: unexpected char: '\' @ line 33, column 24.
       def shellString = "s/\[\|]\|\s\|'\|(\|)//g"
                            ^
  
  1 error
  
      at org.codehaus.groovy.control.ErrorCollector.failIfErrors(ErrorCollector.java:310)
      at org.codehaus.groovy.control.ErrorCollector.addFatalError(ErrorCollector.java:150)
      at org.codehaus.groovy.control.ErrorCollector.addError(ErrorCollector.java:120)
      at org.codehaus.groovy.control.ErrorCollector.addError(ErrorCollector.java:132)
      at org.codehaus.groovy.control.SourceUnit.addError(SourceUnit.java:350)
      at org.codehaus.groovy.antlr.AntlrParserPlugin.transformCSTIntoAST(AntlrParserPlugin.java:139)
      at org.codehaus.groovy.antlr.AntlrParserPlugin.parseCST(AntlrParserPlugin.java:110)
      at org.codehaus.groovy.control.SourceUnit.parse(SourceUnit.java:234)
      at org.codehaus.groovy.control.CompilationUnit$1.call(CompilationUnit.java:168)
      at org.codehaus.groovy.control.CompilationUnit.applyToSourceUnits(CompilationUnit.java:943)
      at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:605)
      at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581)
      at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:558)
      at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298)
      at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268)
      at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688)
      at groovy.lang.GroovyShell.parse(GroovyShell.java:700)
      at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.doParse(CpsGroovyShell.java:131)
      at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell.reparse(CpsGroovyShell.java:125)
      at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.parseScript(CpsFlowExecution.java:560)
      at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.start(CpsFlowExecution.java:521)
      at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:330)
      at hudson.model.ResourceController.execute(ResourceController.java:97)
      at hudson.model.Executor.run(Executor.java:429)
  </code></pre>
  
  <p><code>shellString</code> isn't a slashed string, so not sure why a <code>\</code> would create a problem. Any help is appreciated.</p>