Jenkinsfile ${steps.env.BUILD_NUMBER}: bad substitution

Question

I am trying to print a variable in Jenkins. But I am getting an error saying "bad substitution". I am using Jenkinsfile to achieve that. This is what I am doing.

static def printbn() {
    sh '''
            #!/usr/bin/env bash

            echo \"${env.BUILD_NUMBER}\"
    '''
}

pipeline {
    agent any
        stages {
            stage('Print Build Number') {
                steps {
                    printbn()
                }
            }
        }
}

Error that I am getting

/var/lib/jenkins/workspace/groovymethod@tmp/durable-7d9ef0b0/script.sh: line 4: ${steps.env.BUILD_NUMBER}: bad substitution

NOTE: I am using Jenkins version Jenkins ver. 2.163

Answer 1

In Shell, variable name is not allow use ., that's why you get following error: bad substitution

In Groovy, there are 4 ways to represent a string:

1. single quote: ' a string '
2. tripe single quote: ''' a string '''
3. double quote: " a string "
4. tripe double quote: """ a string """

And Groovy only execute string interpolation on double and triple double quote string.

For example:

def name = 'Tom'

print "Hello ${name}"
print """Hello ${name}"""  
// do interpolation before print, thus get Hello Tom printed out

print 'Hello ${name}' 
print '''Hello ${name}'''
//no interpolation thus, print Hello ${name} out directly.

BUILD_NUMBER is Jenkins job's build-in environment variable. You can directly access it in shell/bat.

static def printbn() {
    sh '''
    #!/usr/bin/env bash

    echo ${BUILD_NUMBER} 
    // directly access any Jenkins build-in environment variable,
    // no need to use pattern `env.xxxx` which only works in groovy not in shell/bat
    '''
}

If you want use env.xxxx pattern, you can archive that via groovy string interpolation.

static def printbn() {

    // use pipeline step: echo
    echo "${env.BUILD_NUMBER}" // env.BUILD_NUMBER is groovy variable 

    // or use pipeline step: sh
    sh """#!/usr/bin/env bash
      echo ${env.BUILD_NUMBER} 
    """
    // will do interpolation firstly, to replace ${env.BUILD_NUMBER} with real value
    // then execute the whole shell script.
}