Store the console output of a build step execution

Question

In my jenkins pipeline i use the "Execute shell command " to run my gradle build script. Now i want to check if the build has failed in which case i would like to read the console output, store it in a string and publish it to a slack channel. The code that i have tried goes as follows :

try {
    for (int i = 0 ; i < noOfComponents ; i++ ){
        component = compileProjectsWithPriority[i]
        node {       
            out = sh script: "cd /home/jenkins/projects/${component} && ${gradleHome}/bin/gradle build", returnStdout: true}
    }
}
catch (e){
    def errorSummary = 'Build failed due to compilation error in '+"${component}"+'\n'+"${out}"
    slackSend (channel: '#my_channel', color: '#FF0000', message: errorSummary)
}

However it does not even execute the shell script and also the console output is null. What is the right approach to do this.

Thanks in advance