Error while Executing Unix Shell Commands Using Runtime clas

Question

I am trying to run the following code in java on unix machine to execute cat command.
Runtime runtime = Runtime.getRuntime();
          try {
               System.out.println("before catexecute");
               Process process = runtime.exec("cat /export/home/shankerr/local.profile > /export/home/shankerr/local1.txt");
               try {
                    if (process.waitFor() != 0) {
                    System.err.println("exit value = " +
                              process.exitValue());
                    catch (InterruptedException e) {
                    System.err.println(e);
But i get the following error on the console
exit value = 2
cat: cannot open >
cat: cannot open /export/home/shankerr/local1.txt
The same command if i run on unix console directly it creates a new file and copies the content into the new file local1.txt
kindly help me on the same

Answer 1

The redirection operator > along with stuff like pipe | history !$ etc. is interpreted by the shell, not by the cat program.
When you do cat X > Ycat only sees the X. The rest is interpreted by the shell to redirect the cat program's stdout.
However, when you Runtime.exec(), you don't have the shell, so cat sees X > Y as its arguments, and interprets them all as file names. Since there's no file named > you get the error.
The solution is to first man cat on your system and see if it happens to have a -o or somesuch operator that lets it (rather than the shell) send its output to a file. If not, then you need to invoke a shell, and pass it cat and all of cat's args as the command to execute.
Read the man pages for you shell of choice, but for bash, I believe you'd give Runtime.exec() something like /bin/bash -c 'cat X > Y'