Java Runtime.getRuntime().exec(cmd) comman

问题:

I need to use Java to rsync several files using one command the following command works fine in shell rsync -avrz --timeout=100 rsync://10.149.21.211:8730/'logflow/click/file1 logflow/click/file2' /home/kerrycai/puller"

but when i use the following Java code , it does not work

String cmd = "rsync -avrz --timeout=100 rsync://10.149.21.211:8730/'logflow/click/file1 logflow/click/file2' /home/kerrycai/puller";
Process p = Runtime.getRuntime().exec(cmd);
int ret =  p.waitFor();

the ret value is not equal to 0 (5 in my test), and the command is not executed succeed, after some debugging , it seem the problem is caused by the single quote

So, my questions is

1. Can I using java to execute a shell command which has single quote in it (Pls note, the single quote is in the middle of a parameter, not start/end) ?
2. Can I have a shell command to rsync several files in one command , and the command does not have single(double) quotes in it ?

回答1:

Note to @Chris: this combination of multiple filenames (really modified-partly-like-filenames) in one argument is indeed very unusual and even 'suspicious' for Unix in general, but is (or at least was) correct for rsync in particular.

Preface: Java Runtime.exec does NOT 'execute a shell command' (unless you explicitly run a shell and give it a command); it runs a program, with arguments. These different things are often confused because most of the shell commands used by normal users are commands to run programs, but this is one case where the difference matters. In particular quoting a space to shell causes the shell to pass a single argument to the program containing the space instead of splitting into two (or more) arguments, but the quote itself is NOT included in the argument.

First you should look at the man page (on your system or online at https://download.samba.org/pub/rsync/rsync.html) under ADVANCED USAGE. Current (and IME even moderately old) versions of rsync have a more convenient syntax with separate arguments to get multiple files, which the simple parsing used by Runtime.exec(String) can handle like this:

rsync -avrz --timeout=100 --port=8730 10.149.21.211::logflow/click/file1 ::logflow/click/file2 /home/kerrycai/puller

But if you need (or really want) to use the quoted-space form then you need to do the tokenization yourself and use the String[] overload as suggested by @EJP -- although you can still use Runtime, you don't need ProcessBuilder for this. Specifically do something along the lines of:

String[] cmdarray = {"rsync",
    "-avrz",
    "--timeout=100",
    "rsync://10.149.21.211:8730/logflow/click/file1 logfile/click/file2",
    // separated argument contains space but not single (or other) quote
    "/home/kerrycai/puller" };
... Runtime.getRuntime.exec(cmdarray); ...

回答2:

You're calling a somewhat large command from Java. Why not just use a shell script? Put your gnarly command in myScript.sh and then have Java invoke /bin/bash myScript.sh. Makes all the weirdness to do with string handling in Java go away.