Help Please: How to invoke unix command lines from java?

Question

I have read past topics. Those are really helpful, but I still haven't got my job done. I tried the following:
String command1 = "ls -la > ls1.txt";
Runtime.getRuntime().exec(command1);
String command2 = "tcsh -c ls -la > ls2.txt";
Runtime.getRuntime().exec(command2);
String command4 = "cp keywords.txt copyversion1.txt";
Runtime.getRuntime().exec(command4);
String command5 = "tcsh -c cp keywords.txt copyversion2.txt";
Runtime.getRuntime().exec(command5);
String command6 = "tcsh -c 'cp keywords.txt copyversion3.txt'";
Runtime.getRuntime().exec(command6);
Only "command4" works. Any input will be greatly appreciated.

Answer 1

Thank you very much Gautam. Your solution certainly works. If you don't mind, I would like to ask you (or anybody who is willing to answer) something else. I am trying to run other types of unix command lines as well. I thought that the format you gave would work for everything. But it doesn't seem so:
String command1[] = {"tcsh", "-c", "ls -la > ls1.txt "}; // this works as you suggested
Runtime.getRuntime().exec(command1);
String command12[] = {"tcsh", "-c", "lynx -dump http://www.yahoo.com > webpage.txt"}; //working fine.
Runtime.getRuntime().exec(command12);
String command10[] = {"tcsh", "-c", "ngram-count -text keywords.txt -lm LM10 &"}; //doesn't work
Runtime.getRuntime().exec(command10);
String command[] = {"tcsh", "-c", "/u/drspeech/sun4/bin/ngram-count -text keywords.txt -lm LM0 &"}; // doesn't work
Runtime.getRuntime().exec(command);
String command13[] = {"tcsh", "-c", "ngc -text keywords.txt -lm LM13"}; // doesn't work
Runtime.getRuntime().exec(command13);
String command8 = "ngram-count -text keywords.txt -lm LM8 &"; //doesn't work
Runtime.getRuntime().exec(command8);
String command9 = "/u/drspeech/sun4/bin/ngram-count -text keywords.txt -lm LM9 &"; //doesn't work
Runtime.getRuntime().exec(command9);
I tried "commandd1" and "command12". Those worked fine. No problemo. However, there's someting else I need to get done for my job; that is "command10". But it just didn't work. I thought maybe, it's because "ngram-count" is not part of the standard UNIX commands. So, I thought I might just add another alias for it in the ".cshrc" file and call it "ngc" instead. Then I tried to call the alias "ngc" instead. But it didn't work also. Then I thought, maybe, I should call it by referencing it from its original directory "/u/drspeech/sun4/bin/ngram-count". That didn't work either. I tried a couple of other combinations. None worked. I would really like to see how to solve this.