C system() equivalent method. (original) (raw)

Martin Buchholz martinrb at google.com
Thu Oct 15 17:59:09 UTC 2009

Hi Frédéric,

Thanks for your suggestion.

The JDK has long had a culture of pushing people to write portable code, and so any facility that would make it easier to interact with the operating system in a non-portable way meets resistance.

Another issue is that the "default" C system shell tends to become dated over time - there are often better command interpreters.

Nevertheless, the existence of C "system" and the "shell" keyword arg to python's subprocess.Popen are strong arguments that the concept of a default shell is entrenched in the programmer community.

Therefore, I support this proposal in principle.

Would someone at Sun like to sponsor this API change? The spec probably needs a bit more work, so that readers will know that we're talking about e.g. /bin/sh without making that explicit.

Martin

2009/9/17 Frédéric Martini <frederic.martini at gmail.com>:

Hello (before to start, sorry for my bad english)

I have seen in the last JDK's build that ProcessBuilder allow to manage the process I/O more efficiently. In particular, the inheritIO() set the subprocess standard I/O to be the same as those of the current Java process, and offer a behavior "equivalent" to the standard C library function system(). This is very great an usefull ! But there is another BIG difference between ProcessBuilder and the C library function system() : ProcessBuilder execute an application, and C system() evaluate a command-line using the OS's shell. So C's system() can use a lot of OS's specific syntax ($ENV or %ENV%, * ?, pipe, redirect, etc...) witch is incorrect on a ProcessBuilder (because this syntax is not interpreted but directly passed to the application). This is a common misunderstanding for Java's developer... My proposal simply consist to add a method that create a ProcessBuilder pre-filled with a shell command's line, by invoking the OS's shell ("/bin/sh" on Unixes, "command.com" on Win9x, "cmd.exe" on WinNT, etc. ? ) in order to evaluate a more complex command-line. A "basic" implementation can be like this : ====================================================================== /**  * Create a new ProcessBuilder initialized to call an OS's  * specific command-line.  */ public static ProcessBuilder createShellFor(String commandLine) { String osName = System.getProperty("os.name"); if (osName.startsWith("Windows")) { if (osName.startsWith("Windows 95") ||  osName.startsWith("Windows 98") ||  osName.startsWith("Windows Me") ) { return new ProcessBuilder("command.com", "/C", commandLine); } return new ProcessBuilder("cmd.exe", "/C", commandLine); } return new ProcessBuilder("/bin/sh", "-c", commandLine); } ====================================================================== This method can be improved with more specific code depending on OS.

And a "system()" method with a behavior really equivalent to the standard C library function system(), like this : ====================================================================== /**  * Executes a command specified in 'commandLine' by calling  * the OS shell program, and returns after the command has been completed.  * @param commandLine The command-line to execute, using OS shell.  * @return the exit value of the subprocess  */ public static int system(String commandLine) throws IOException, InterruptedException { final Process process = createShellFor(commandLine).inheritIO().start(); try { return process.waitFor(); } finally { process.destroy(); } } ====================================================================== So, more complex and specific command-line can be used directly, like in lots of others languages... Thanks for reading, Fred

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