why if [[ ]] not working when writing shell script inside groovy-CodePudding

CASE1:when running following shell script inside Jenkins pipeline:

pipeline
{ 
agent any
  stages
  {

   stage('image')
        
        { 
        
    steps {
            
            script {
            sh (  returnStdout: true,
                 script: ''' #!/bin/bash
                             if [[ 56 > 10 ]]
                             then
                             echo 'The variable is greater than 10.'
                             fi
                         '''
           
            ) }
            }
          } 
        }
}

the above throws an exception:

/var/lib/jenkins/workspace/test-job@tmp/durable-f9ee86ef/script.sh: 2: [[: not found

CASE2: But following pipeline works perfectly fine:

pipeline
{ 
agent any
  stages
  {

   stage('image')
        
        { 
        
    steps {
            
            sh  '''#!/bin/bash
                    VAR=56
                    if [[ $VAR -gt 10 ]]
                    then
                     echo "The variable is greater than 10."
                    fi
              '''
          } 
        }
      }

}

kindly please explain to me why the same shell script works in the above CASE2 while it fails in CASE1?

CodePudding user response：

First script starts with

script: ''' #!/bin/bash

Note that there is a space between ''' and #. Only if the first two bytes of a script are #!, this pattern is recognized and defines the shell to use. If it is anything else, including <space>#!, it is not recognized and the default shell is used. And unless that default shell is bash, [[ is not valid. In POSIX shells, only [ is valid.

The reason why the second script works correctly is because there is no space between ''' and #.