I'm currently working on invoking bash program using java. The bash program output too much message and I want to redirect them to /dev/null. But I encountered a weird error No such file or directory.
Here is my demo.
public static void main(String[] args) {
try {
// Another version I've tried:
// Process p = Runtime.getRuntime().exec("echo a > /dev/null");
ProcessBuilder b = new ProcessBuilder("echo a");
// b.redirectOutput(new File("/dev/null")).redirectErrorStream(true);
b.redirectOutput(ProcessBuilder.Redirect.to(new File("/dev/null")))
.redirectErrorStream(true);
Process p = b.start();
p.waitFor();
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
}
And the error message as follows:
java.io.IOException: Cannot run program "echo a": error=2, No such file or directory
at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1128)
at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1071)
at test.main(test.java:12)
Caused by: java.io.IOException: error=2, No such file or directory
at java.base/java.lang.ProcessImpl.forkAndExec(Native Method)
at java.base/java.lang.ProcessImpl.<init>(ProcessImpl.java:340)
at java.base/java.lang.ProcessImpl.start(ProcessImpl.java:271)
at java.base/java.lang.ProcessBuilder.start(ProcessBuilder.java:1107)
... 2 more
I'm using a MacBook with Catalina, and I tried java 1.8.0_231 and 1.8.0_241 from oracle. (I couldn't use higher java version because one of the dependency of my project requires java 8).
To ignore the output from the process, it's easier and more portable to use ProcessBuilder.Redirect.DISCARD than explicitly redirecting to a special file/device such as /dev/null.
b.redirectOutput(ProcessBuilder.Redirect.DISCARD)
.redirectErrorStream(true);
Forget about using Runtime.exec - that method is badly designed and hard to use safely. If you want to do input redirection with the "> /dev/null" style, you need to remember that > is a construct created by the command interpreter shell, not the operating system, and if you want to use it you must run a shell.
Runtime.getRuntime().exec(new String[] {"sh", "-c", "echo a > /dev/null"});