在 Eclipse 中启动程序与在终端中启动它有何不同？

Question

I have a bit of code which works fine when launched from a terminal, but not when launched from within eclipse. Clearly, I can just use the terminal, but for debugging purposes it would be nice to sort the issue out. Further, it would be nice to understand the issues at play. Can anyone explain point me to an explanation of how launching within eclipse differs from launching in a terminal. Code:

static public Process getNewLiEProcess(boolean redirect){
    ProcessBuilder proc = new ProcessBuilder("lie");
    proc.redirectErrorStream(redirect);
    try {
    return proc.start();
    // TODO: figure out why this consistently fails when run in Eclipse console, 
    // even though it seems to work when run in terminal.
    } catch (IOException e) {


    e.printStackTrace();
    return null;
    }
}

Error message when launched in Eclipse:

java.io.IOException: Cannot run program "lie": error=2, No such file or directory
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1047)
    at edu.siu.math.egut.io.LiE.getNewLiEProcess(LiE.java:224)
    at edu.siu.math.egut.io.LiE.<init>(LiE.java:198)
    at edu.siu.math.egut.main.CharacterAction.main(CharacterAction.java:106)
Caused by: java.io.IOException: error=2, No such file or directory
    at java.lang.UNIXProcess.forkAndExec(Native Method)
    at java.lang.UNIXProcess.<init>(UNIXProcess.java:184)
    at java.lang.ProcessImpl.start(ProcessImpl.java:130)
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1028)
    ... 3 more
Exception in thread "main" java.lang.NullPointerException
    at edu.siu.math.egut.io.LiE.<init>(LiE.java:202)
    at edu.siu.math.egut.main.CharacterAction.main(CharacterAction.java:106)

When launched using terminal, same code successfully instantiates a "lie" process (the program "lie" is in usr/bin on my system).

Answer 1

The difference can come from:

• the java binary used to execute the program
• environment variables, especially CLASSPATH , JAVA_HOME , PATH , LD_LIBRARY_PATH (to name just a few)
• the various flags passed to java
• working directory

It's important that you fully understand at all times the requirements of your program in terms of the above factors. Once you know all that, it's a matter of verifying that the requirements are correctly setup, whether you execute from the command line and from Eclipse.

If you can make things work on the command line, then the hard part is done. On the command line it's very easy to verify your environment:

• java -version to verify the java binary in use
• env | sort | less env | sort | less to verify the environment variables in use
• the flags passed to java are right there in the command you execute
• pwd to verify the working directory

Usually it's harder to figure things out the other way around, when things work from Eclipse but not from the command line. Verifying the same details requires a good understanding of Eclipse, and where things are in the menus and project and launcher settings.