Using nested command substitution in jenkins pipeline sh step

Question

I'm trying to flatten a results directory prior to archiving using a symbolic link to the relevant inner folder that first traverses a bunch of variable path names determined at runtime. I can't quite seem to get the syntax right with this command substitution approach I picked up from this SO answer.

Question: is there a rule for how to properly escape command substitution chains from a Jenkins pipeline step that I'm unaware of?

Pipeline Script snippet

post {
  always {   
    sh """
    echo 'Link to inner output result folder to make the artifacts more shallow'
    echo ln -sf dirname find $output_dir -name $jUnitResult $WORKSPACE/$output_dir_inner
    ln -sf $(dirname $(find ${output_dir} -name ${jUnitResult})) $WORKSPACE/$output_dir_inner
    """

    archiveArtifacts output_dir_inner
  }
}

Console Output

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 52: illegal string body character after dollar sign;
   solution: either escape a literal dollar sign "\$5" or bracket the value expression "${5}" @ line 52, column 21.
               ln -sf $(dirname $(find ${output_dir} -name ${jUnitResult})) $WORKSPACE/$output_dir_inner
                       ^

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)
Finished: FAILURE

I see a similar failure when attempting

Pipeline Script snippet

ln -sf $(dirname $(find $output_dir -name $jUnitResult)) $WORKSPACE/$output_dir_inner

Console Output

org.codehaus.groovy.control.MultipleCompilationErrorsException: startup failed:
WorkflowScript: 49: illegal string body character after dollar sign;
   solution: either escape a literal dollar sign "\$5" or bracket the value expression "${5}" @ line 49, column 13.
               sh """
               ^

Answer 1

Couple of interesting strategies around this problem

Decompose long sh scripts into distinct functional pieces with return values

https://stackoverflow.com/a/47394132/1330381

Escape nested shell commands with backslash \$,

sh """
    \$(echo TEST this subshell \$(ls .))
"""

https://stackoverflow.com/a/50356318/1330381