如何通过在Tomcat7中运行的Grails应用程序执行shell命令？

Question

以下代码仅适用于我的开发环境。但是，它会在生产中引发错误（如下所述）。

class ThemeBuilder {

  def compileTheme(basePath, courseID, desiredColor) {
    def outputCSSFilename = basePath + 'themes/' + courseID.toString() + '.css'
    def tmpFilename = basePath + courseID.toString() + '_tmp.scss'
    def sourceFilename = basePath + 'theme-builder-source.scss'

    def source = new File(sourceFilename)
    def tmp = new File(tmpFilename)

    def pattern = ~/^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$/
    def matches = pattern.matcher(desiredColor).matches()

    // Checks existence of the path for themes
    def dir = new File(basePath + 'themes')
    if (! dir.exists()) dir.mkdirs()

    // Validate color
    if (!matches) desiredColor = '#4F9C91'

    // Replace placeholder color with desired color
    tmp.withWriter { w ->
      source.eachLine { line ->
        w << line.replaceAll('brand-primary: #F7DC40', 'brand-primary: ' + desiredColor) + System.getProperty('line.separator')
      }
    }

    // Compilation process
    def cmd = 'sass ' + tmpFilename + ' ' + outputCSSFilename + ' --style compact'
    def result = cmd.execute()
    result.waitFor()

    //////////////// Debugging ////////////////
    // println "Text output: ${ result.text }"
    // println "Return code: ${ result.exitValue() }"
    // println "stderr: ${ result.err.text }"
    // println "stdout: ${ result.in.text }"
    //////////////////////////////////////////

    // Remove tmp file
    tmp.delete()
  }

}

错误：

2014-10-22 14:41:28,886 [http-bio-8080-exec-19] ERROR errors.GrailsExceptionResolver  - IOException occurred when processing request: [PUT] /pemaap/course/update
error=2, No such file or directory. Stacktrace follows:
java.io.IOException: error=2, No such file or directory
        at java.lang.UNIXProcess.<init>(UNIXProcess.java:186)
        at java.lang.ProcessImpl.start(ProcessImpl.java:130)
        at java.lang.ProcessBuilder.start(ProcessBuilder.java:1028)
        at java.lang.Runtime.exec(Runtime.java:617)
        at java.lang.Runtime.exec(Runtime.java:450)
        at java.lang.Runtime.exec(Runtime.java:347)
        at br.com.tokenlab.pemaap.ThemeBuilder.compileTheme(ThemeBuilder.groovy:32)

请注意，问题从第32行开始，与行def result = cmd.execute()完全对应。

我无法检查tomcat7用户（ps aux | grep tomcat）是否能够执行root用户安装的sass，或者实际上是否缺少某些必需文件。有没有人经历过这个？

Obs：服务器在Ubuntu 14.04.1 LTS上运行。