How to use exec() output in gradle

Gradle Problem Overview

I am trying to implement a gradle task to dynamically create a buildsignature.properties file from a series of environment variable values and shell executions. I have it mostly working, but I can't seem to get the output of the shell commands. Here's my task...

task generateBuildSignature << {
    ext.whoami = exec() {
        executable = "whoami"
    }
    ext.hostname = exec() {
         executable = "hostname"
    }
    ext.buildTag = System.env.BUILD_TAG ?: "dev"

    ant.propertyfile(
        file: "${buildDir}/buildsignature.properties",
        comment: "This file is automatically generated - DO NOT EDIT!" ) {
        entry( key: "version", value: "${project.version}" )
        entry( key: "buildTimestamp", value: "${new Date().format('yyyy-MM-dd HH:mm:ss z')}" )
        entry( key: "buildUser", value: "${ext.whoami}" )
        entry( key: "buildSystem", value: "${ext.hostname}" )
        entry( key: "buildTag", value: "$ext.buildTag" )
    }
}

But the resulting properties field does not get the desired results for buildUser and buildSystem.

#This file is automatically generated - DO NOT EDIT!
#Mon, 18 Jun 2012 18:14:14 -0700
version=1.1.0
buildTimestamp=2012-06-18 18\:14\:14 PDT
buildUser=org.gradle.process.internal.DefaultExecHandle$ExecResultImpl@2e6a54f9
buildSystem=org.gradle.process.internal.DefaultExecHandle$ExecResultImpl@46f0bf3d
buildTag=dev

How do I get buildUser and buildSystem to match the output of the corresponding exec rather than some default ExecResultImpl toString? This really can't be that hard, can it?

Gradle Solutions

Solution 1 - Gradle

This is my preferred syntax for getting the stdout from exec:

def stdout = new ByteArrayOutputStream()
exec{
	commandLine "whoami"
	standardOutput = stdout;
}
println "Output:\n$stdout";

Found here: http://gradle.1045684.n5.nabble.com/external-process-execution-td1431883.html (Note that page has a typo though and mentions ByteArrayInputStream instead of ByteArrayOutputStream)

Solution 2 - Gradle

This post describes how to parse the output from an Exec invocation. Below you'll find two tasks that run your commands.

task setWhoamiProperty {
    doLast {
        new ByteArrayOutputStream().withStream { os ->
            def result = exec {
                executable = 'whoami'
                standardOutput = os
            }
            ext.whoami = os.toString()
        }
    }
}

task setHostnameProperty {
    doLast {
        new ByteArrayOutputStream().withStream { os ->
            def result = exec {
                executable = 'hostname'
                standardOutput = os
            }
            ext.hostname = os.toString()
        }
    }
}

task printBuildInfo {
    dependsOn setWhoamiProperty, setHostnameProperty
    doLast {
         println whoami
         println hostname
    }
}

There's actually an easier way to get this information without having to invoke a shell command.

Currently logged in user: System.getProperty('user.name')

Hostname: InetAddress.getLocalHost().getHostName()

Solution 3 - Gradle

Using the kotlin-dsl:

import java.io.ByteArrayOutputStream

val outputText: String = ByteArrayOutputStream().use { outputStream ->
  project.exec {
    commandLine("whoami")
    standardOutput = outputStream
  }
  outputStream.toString()
}

Solution 4 - Gradle

Groovy allows for a much simpler implementation in many cases. So if you are using Groovy-based build scripts you can simply do this:

def cmdOutput = "command line".execute().text

Solution 5 - Gradle

Paraphrased from the Gradle docs for Exec:

task execSomething {
  doFirst {
    exec {
      workingDir '/some/dir'
      commandLine '/some/command', 'arg'

      ...
      //store the output instead of printing to the console:
      standardOutput = new ByteArrayOutputStream()

      //extension method execSomething.output() can be used to obtain the output:
      ext.output = {
        return standardOutput.toString()
      }
    }
  }
}

Solution 6 - Gradle

kotlin-dsl variants

Groovy style

in buildSrc:

import org.codehaus.groovy.runtime.ProcessGroovyMethods

fun String.execute(): Process = ProcessGroovyMethods.execute(this)
fun Process.text(): String = ProcessGroovyMethods.getText(this)

build.gradle.kts:

"any command you want".execute().text().trim()

exec style