Executing an exe from a java program

[Uma Viswanathan]

I want to execute an exe file (say, a.out) in hp-ux 10.20 from the java program.

1) The java code
Runtime.getRuntime().exec(". ./a.out");
is NOT WORKING

2) The java code
Runtime.getRuntime().exec("a.out");
is NOT WORKING

3) I wrote a script (say, test)
#!/bin/sh
a.out
Then i called this script from the java program
Runtime.getRuntime().exec("test");
This is also NOT WORKING
4) I wrote a script (say, test)
a.out
Then i called this script from the java program
Runtime.getRuntime().exec(new String[] {"/bin/sh", "test"});
This code is WORKING
Could someone please explain me why the codes (1, 2 and 3) are not working and why the code 4 is working...Thanks a lot...

[Frank Carver]

My guess is that it is one of two problems:

you may have assumed the wrong "current directory". Notice that the only one which works is the one with a full path to "/bin/sh". Can you try one of the other examples but using the full path to the executable, ie "/home/someone/tests/a.out" or whatever ?

you may have forgotten to make your examples executable. Remember that for any *nix system to execute a binary or script file it needs to have the "x" bit set for an appropriate user. Try ls -l a.out and look for something like rwxr-xr-x . If there are no 'x' characters, try chmod 755 a.out then try to execute it again.

Please let us know how you get on.

[Uma Viswanathan]

Hi Frank Carver:
Thank you very much for your reply.
I tried with full path...it is working fine. Once again, thanks.
But i have a doubt now
1) Runtime.exec("java MyExample") works fine...where MyExample is a .class file in the directory /home/someone/test. It is WORKING FINE WITHOUT GIVING FULL PATH
2) Runtime.exec("a.out") is not working...where a.out is an exe file in the directory /home/someone/test. It is NOT WORKING WITHOUT GIVING FULL PATH
3) Runtime.exec("/home/someone/test/a.out") is working...where a.out is an exe file in the directory /home/someone/test. It is WORKING BY GIVING FULL PATH
Could you please explain me what is happening in all the three cases.
Also please explain the code 3 and 4 what i had written yesterday...
Waiting for your reply to understand the concepts behind it.
Thanks a lot.
Uma

[Frank Carver]

This situation arises because your current directory is not in your PATH, whereas the directory containing the "java" executable is in the PATH.
type echo $PATH to see what is in your path.
On most modern *nix systems, the current directory (.) is not in the PATH, as it is seen to present too much of a security risk. You might be able to get this working without a full path by using . as the path for the command ie.:
Runtime.getRuntime().exec("./a.out");
This is almost like your original example 1, but doesn't have the leading "." and space, which only work in the context of a shell.

[Uma Viswanathan]

Hi Frank Carver:
Please do confirm the following:
1) I had written "The code Runtime.getRuntime().exec("a.out") is not working...where a.out is an exe file in the directory /home/someone/test. It is NOT WORKING WITHOUT GIVING FULL PATH"
The reason is: Runtime.getRuntime().exec tries to search the a.out in the home directory...i tested by copying the a.out to the home directory and execute the above code. It works fine.

2) I had written
"I wrote a script (say, test)
#!/bin/sh
a.out
Then i called this script from the java program
Runtime.getRuntime().exec("test"); This is also NOT WORKING"
The reason is: Runtime.getRuntime().exec does not spawn a shell but we need a shell to run the script.
The test script above (which contains the command #!/bin/sh) does not spawn a shell...so, it is not working.
3) I had written
"I wrote a script (say, test)
a.out
Then i called this script from the java program
Runtime.getRuntime().exec(new String[] {"/bin/sh", "test"}); This code is WORKING"
The reason is: This works bcoz the first parameter to exec (i.e., /bin/sh) spawns a shell.
Frank Carver: please confirm whether my understanding is correct or not....Also add your views/points...
4) I had written "Runtime.exec("/home/someone/test/a.out") is working...where a.out is an exe file in the directory /home/someone/test. It is WORKING BY GIVING FULL PATH"
Here we are hard coding the directory name, which will not be good in a project. So, could you please tell me the way to specify the directory name.
Thanks a lot.
Uma

[Uma Viswanathan]

Sorry..i did not see ur previous reply when i had posted my earlier one...i typed the message and then it was time to go for the meeting...after i came back...i just clicked "Add reply"...

[Frank Carver]

No problem. I'm sure we all do that from time to time. Please let me know if my other suggestion does work, though.

[Uma Viswanathan]

Hi Frank Carver:
Thanks for your reply.
Runtime.getRuntime().exec("./a.out"); is not working
but it is working if i include . (i.e, current directory) in the PATH.
Also i am able to run the exe thru a script.
Thanks a lot for your ideas.
Uma