capture process output in Groovy

Question

I have a Groovy script that recurses through a directory looking for .png files, and invokes pngquant (a command-line utility) on each of. The output of pngquant should be printed on the terminal. The relevant code is:

def command = "pngquant -f -ext .png"

root.eachFileRecurse(groovy.io.FileType.FILES) {File file ->

    if (file.name.endsWith('.png')) { 
        println "Compressing file: $file"

        def imgCommand = "$command $file.absolutePath"

        Process pngquantCmd = imgCommand.execute()
        pngquantCmd.consumeProcessOutput(System.out, System.err)        
    }
}

The script works fine, but once all the files have been processed, it seems that stout is still being redirected, because the command-prompt never appears unless I kill the process with Ctrl + C. Do I need to somehow "undo"

pngquantCmd.consumeProcessOutput(System.out, System.err)        

or is there a better way to redirect the output of this process to the console? I guess I could solve this problem simply by adding System.exit(0), but this doesn't seem like the right solution. The problem only occurs on Linux.

Answer 1

Instead of

    pngquantCmd.consumeProcessOutput(System.out, System.err)        

Which will start a couple of threads to read the outputs and plough on regardless of the process' situation, you should try

    pngquantCmd.waitForProcessOutput(System.out, System.err)

Which will redirect the process output and then wait for it to finish before moving on :-)

Answer 2

You can also do

Process pngquantCmd = imgCommand.execute();
def output= pngquantCmd.text;
println("Output : " + output);