Groovy Process Piping

I was playing around with using Groovy as a shell scripting language. While convenient, I found that shelling out to my trusted unix commands is many times faster for file operations than handling them within Groovy.

Creating and executing a process is trivial in groovy:

p = "ls -l".execute()
println p.text

But using pipes or redirection is not allowed:

p = "ls -l | sort".execute()
println p.text

For some reason it took me awhile to understand the java.lang.Process well enough to come up with this script, which contains a helper class for piping one Unix shell command into another.

def class Pipe {
   private Process p

   def Pipe(cmd) {
       p = cmd.execute()
       p.out.close()
   }

   def to(cmd) {
       def p2 = cmd.execute()
       p2.out << p.in
       p2.out.close()
       p = p2
       this
   }

   def text() {
       p.text
   }
}

def output = new File('output.txt')
output.delete()

output << new Pipe("grep -h -e '^.* ERROR .*' input.txt")
   .to("sort")
   .to("tail -n50").text()

Note 1: The Process object is in the standard JDK so with a bit of alteration, one could create the Pipe utility in straight-up Java. But in regular Java I wonder how often one needs to run a shell command?

Note 2: If you are on Windows and are using Cygwin you'll need to be aware that the Windows "sort" command clobbers the Unix version and is hardly as robust. You may need to hard code which sort you want to use: "C:\\cygwin\\bin\\sort"