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Runtime.getRuntime().exec(cmd) issues

13 replies on 1 page. Most recent reply: Jul 6, 2007 1:14 AM by Anne van Rossum

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Flat View: This topic has 13 replies on 1 page
Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Runtime.getRuntime().exec(cmd) issues Posted: Jun 20, 2007 1:24 PM
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I want to use java to telnet into a server and do stuff there, I have the following code below:
the "telnet server" part doesn't seem to do anything.

try {
p= Runtime.getRuntime().exec(cmd);
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
writer.write("telnet server\n");
writer.flush();
writer.close();
while ((line = reader.readLine()) != null) {
System.out.println(line); //reading from process
}
} catch (IOException e) {
e.printStackTrace();
}
}


Matthias Neumair

Posts: 660
Nickname: neumi
Registered: Sep, 2003

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 21, 2007 6:59 AM
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Well, I don't know what the content of cmd is, but when I used "cmd" instead, "telnet server" war written on the standard output writer.

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 21, 2007 7:00 AM
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Sorry I meant
try {
p= Runtime.getRuntime().exec("cmd");
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(p.getOutputStream()));
writer.write("telnet server\n");
writer.flush();
writer.close();
while ((line = reader.readLine()) != null) {
System.out.println(line); //reading from process
}
} catch (IOException e) {
e.printStackTrace();
}
}

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 21, 2007 7:01 AM
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Quote:" Well, I don't know what the content of cmd is, but when I used "cmd" instead, "telnet server" war written on the standard output writer."

"telnet server" is written on the standard output writer, but it doesn't do anything.

Dave H

Posts: 16
Nickname: slebtack
Registered: Apr, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 22, 2007 1:14 AM
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Try writing "telnet server\r" instead of "telnet server\n" ?

Dave Lorde

Posts: 8
Nickname: dlorde
Registered: Aug, 2005

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 25, 2007 6:22 AM
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Normally, to run a task inside a command prompt window using Runtime.exec(..), you append the task name and its arguments to the command string rather than trying to use the output stream.

See http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html and http://java.sun.com/developer/JDCTechTips/2003/tt0304.html#1

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 26, 2007 1:26 PM
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For example, if I have username :testUser and password:testPassword.

What would be the code that can telnet me into server?

Thanks

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 27, 2007 6:38 AM
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The code I have above works for all commands like
ls, cmd, and even perl perlFile.pl
just doesn't work for telnet.
I am very puzzled.

Dave H

Posts: 16
Nickname: slebtack
Registered: Apr, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 27, 2007 6:50 AM
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What, exactly, do you expect to happen?

What actually happens? You say that it doesn’t work, but you don’t say what it is doing wrong.

You are running on a unix/linux system? What happens when you try commands like which telnet or echo $PATH ?

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 27, 2007 8:42 AM
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If I use
writer.write("pwd\n");
it works, I can see the directory I am and stuff.
However
if I use
writer.write("telnet server\n");
Nothing happens, writer.write("telnet server \t"); doesn't do anything either.
So, it doesn't do anything, I get no output and I am still in the same directory.

What I am trying to do is.
Make a java program that runs in windows.

I am trying to run commands on this unix machine. So, I have to telnet into it first.

Thanks for the help guys.

Dave H

Posts: 16
Nickname: slebtack
Registered: Apr, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 27, 2007 9:22 AM
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When you try running telnet manually from the command line, does that work?

If you run echo %PATH% from the command line, does that give the same output as if you run it from inside java?

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jun 27, 2007 9:46 AM
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If I manually type in telnet server in the command promp, it works. It just does work when I try to use java to run the command.
Are there some sort of permission thing I have get by in order for telnet to work?

Chenen Liang

Posts: 8
Nickname: chenen
Registered: Jun, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jul 4, 2007 6:58 AM
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hello? anybody?

Anne van Rossum

Posts: 1
Nickname: mrquincle
Registered: Jul, 2007

Re: Runtime.getRuntime().exec(cmd) issues Posted: Jul 6, 2007 1:14 AM
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Like already said, place "telnet ..." directly in cmd. Do not just write to stdout.

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