How can I pass a value to the command prompt?

Question

I was wondering how can I pass a value to the command prompt with Windows and Linux? I'm more interested in Linux's system than Windows though. Is there a way to return info from the command prompt?

Answer 1

Here is a snippet from http://mindprod.com/jglossexec.html that explains how in detail.
Runtime.getRuntime().exec("myprog.exe") will spawn an external process that runs in parallel with the Java execution. In Windows 95/98/ME/NT/2000/XP, you must use an explicit *.exe or *.com extension on the parameter. It is also best to fully qualify those names so that the system executable search path is irrelevant, and so you don't pick up some stray program off the path with the same name.
To run a *.BAT, *.CMD, *.html *.BTM or URL you must invoke the command processor with these as a parameter. These extensions are not first class executables in Windows. They are input data for the command processor. You must also invoke the command processor when you want to use the < > | piping options, Here's how, presuming you are not interested in looking at the output:
Runtime.getRuntime( ).exec ("command.com /E:1900 /C MyBat.bat" );
Runtime.getRuntime( ).exec ("cmd.exe /E:1900 /C MyCmd.cmd" );
Runtime.getRuntime( ).exec ("C:\\4DOS601\\4DOS.COM /E:1900 /C MyBtm.btm" );
Runtime.getRuntime( ).exec ("D:\\4NT301\\4NT.EXE /E:1900 /C MyBtm.btm" );
There are also overloaded forms of exec(),
Runtime.getRuntime( ).exec ("command.com /E:1900 /C MyBat.bat", null);
Runtime.getRuntime( ).exec ("command.com /E:1900 /C MyBat.bat", null, "C:\\SomeDirectory");
The second argument can be a String [], and can be used to set environment variables. In the second case, "C:\\SomeDirectory" specifies a directory for the process to start in. If, for instance, your process saves files to disk, then this form allows you to specify which directory they will be saved in.
Windows and NT will let you feed a URL string to the command processor and it will find a browser, launch the browser, and render the page, e.g.
Runtime.getRuntime( ).exec ("command.com http://mindprod.com/projects.html" );
Another lower level approach that does not require extension associations to be quite as well set up is:
Runtime.getRuntime( ).exec ("rundll32 url.dll,FileProtocolHandler http://mindprod.com/projects.html" );
Note that a URL is not the same thing as a file name. You can point your browser at a local file with something like this: file://localhost/E:/mindprod/jgloss.html or file:///E|/mindprod/jgloss.html.
Composing just the right platform-specific command to launch browser and feed it a URL to display can be frustrating. You can use the BrowserLauncher package to do that for you.
Note that
rundll32.exe url.dll,FileProtocolHandler file:///E|/mindprod/jgloss.html
won't work on the command line because | is reserved as the piping operator, though it will work as an exec parameter passed directly to the rundll32.exe executable.
With explicit extensions and appropriately set up associations in Windows 95/98/ME/NT/2000/XP you can often bypass the command processor and invoke the file directly, even *.bat.
Similarly, for Unix/Linux you must spawn the program that can process the script, e.g. bash. However, you can run scripts directly with exec if you do two things:
Start the script with #!bash or whatever the interpreter's name is.
Mark the script file itself with the executable attribute.
Alternatively start the script interpreter, e.g.
Runtime.getRuntime( ).exec (new String[]{"/bin/sh", "-c", "echo $SHELL"}";