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Tip of the Day
Language: Java
Expertise: Beginner
May 1, 1998

System calls

Question:
How can I make shell level calls from a java program? For example, I want to execute the "ls -al" command from java and return its values back to the user. I tried the exec() method of the Runtime class, but it returns a Process which is an abstract class and cannot be instantiated. Is there any other method of doing this?

Answer:
You want to use the Runtime.exec() method after getting a reference to the default Runtime using Runtime.getRuntime(). Just because Process is an abstract class, does not mean that exec() cannot return a valid reference. What exec() does is return a subclass of Process appropriate to the platform you are running on. To read the output from a child process, you must fetch its output stream using getOutputStream().

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