How to deal with pipe in the Java system call?

Question

Hi, all,
I tried to use a system call in java. The command contains a "|" pipe. It works both in perl and C if I do {color:#3366ff}system("ls -l | wc"){color}, but when I do it in Java, I didn't get anything returned. Here is the code
{color:#3366ff}import java.io.*;
class SystemCall{
public static void main(String[] args) throws IOException {
StringBuffer sb = new StringBuffer();
Process p = Runtime.getRuntime().exec("ls -l | wc");
BufferedReader br=new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
while((line=br.readLine())!=null) {
System.out.println(line);
}{color}
If I use Runtime.getRuntime().exec("ls -l"), the code returns correctly. Does anyone know the solution?
Thanks

Answer 1

When you exec a process, it doesn't go through the shell. The I/O redirection symbols are interpreted and used by the shell.
You have a few options.
One is to not use Runtime.exec at all. You really don't need it for what you're doing -- the stuff in java.io is fine for that.
Another is to exec multiple processes and do the redirection in Java yourself. I wouldn't recommend that, but it's an option.
Another is to exec a shell, and pass your program to it as a shell script or as a one-line script passed on the command line.
I'd suggest the first one in this case.
By the way, what you're doing isn't really a "system call". You're forking and exec'ing a process (or really, multiple processes).