Why does 'java -version' go to stderr?

问题

Is there any special reason for the results of java -version going to stderr?

For example, this command executed from Windows' prompt line:

java -version > java_version.txt

leaves the file java_version.txt empty.

EDIT: The same happens with the help printed out after executing java.exe without any parameters.

EDIT: Just out of a sheer curiosity I checked whether it has been always like that and it turned out it actually has. java -version goes to stderr in JDK 1.1.8 and also in JDK 1.2.2, however the outputs of java.exe without any parameters do not.

回答1:

Is there any special reason for the results of java -version going to stderr?

AFAIK, there is no special reason. It is just how the java command was / is implemented. Probably all the way back to Java 1.0, though it would be very difficult to verify that.

My brief investigation shows that this behavior is inconsistent with how most Linux commands behave ... everything else I've tried uses stdout for version information. (After all, the version information is not "error" output.)

Note however --version / -version options are a convention rather than something required by any formal standard. (The GNU coding standards state that commands should implement --version and that version info should be written to standard output. But POSIX standards don't mention this, nor do the LSB standards.)

What can / should you do?

It should be easy to capture stderr instead of stdout in your shell script or batch file.
There shouldn't be any risk in doing this. Oracle cannot change the Java tool chains to send -version output to stdout without potentially breaking customer scripts. This is highly unlikely¹.

^{1 - Here is evidence of just how unlikely it is: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4380614. Note the "Resolution: Wont Fix" ... and the final comment.}

回答2:

The workaround for this problem is:

java -version 2> java_version.txt

来源：https://stackoverflow.com/questions/13483443/why-does-java-version-go-to-stderr

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java

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stderr