Develop Reference

Pipe ("|") doesn't work with ProcessBuilder in Android [duplicate]

I'm trying to use Java's ProcessBuilder class to execute a command that has a pipe in it. For example:
ls -l | grep foo
However, I get an error:
ls: |: no such file or directory
Followed by:
ls: grep: no such file or directory
Even though that command works perfectly from the command line, I can not get ProcessBuilder to execute a command that redirects its output to another.
Is there any way to accomplish this?

This should work:
ProcessBuilder b = new ProcessBuilder("/bin/sh", "-c", "ls -l| grep foo");
To execute a pipeline, you have to invoke a shell, and then run your commands inside that shell.

The simplest way is to invoke the shell with the command line as the parameter. After all, it's the shell which is interpreting "|" to mean "pipe the data between two processes".
Alternatively, you could launch each process separately, and read from the standard output of "ls -l", writing the data to the standard input of "grep" in your example.

Since Java 9, there’s genuine support for piplines in ProcessBuilder.
So you can use
List<String> result;
List<Process> processes = ProcessBuilder.startPipeline(List.of(
new ProcessBuilder("ls", "-l")
.inheritIO().redirectOutput(ProcessBuilder.Redirect.PIPE),
new ProcessBuilder("grep", "foo")
.redirectError(ProcessBuilder.Redirect.INHERIT)
));
try(Scanner s = new Scanner(processes.get(processes.size() - 1).getInputStream())) {
result = s.useDelimiter("\\R").tokens().toList();
}
to get the matching lines in a list.
Or, for Windows
List<String> result;
List<Process> processes = ProcessBuilder.startPipeline(List.of(
new ProcessBuilder("cmd", "/c", "dir")
.inheritIO().redirectOutput(ProcessBuilder.Redirect.PIPE),
new ProcessBuilder("find", "\"foo\"")
.redirectError(ProcessBuilder.Redirect.INHERIT)
));
try(Scanner s = new Scanner(processes.get(processes.size() - 1).getInputStream())) {
result = s.useDelimiter("\\R").tokens().toList();
}
These examples redirect stdin of the first process and all error streams to inherit, to use the same as the Java process.
You can also call .redirectOutput(ProcessBuilder.Redirect.INHERIT) on the ProcessBuilder of the last process, to print the results directly to the console (or wherever stdout has been redirected to).

Run consecutive Commands Linux with java runtime exec

I need to run two commands Linux using java code like this:
Runtime rt = Runtime.getRuntime();
Process pr=rt.exec("su - test");
String line=null;
BufferedReader input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
while((line=input.readLine()) != null) {
System.out.println(line);
}
pr = rt.exec("whoami");
input = new BufferedReader(new InputStreamReader(pr.getInputStream()));
line=null;
while((line=input.readLine()) != null) {
System.out.println(line);
}
int exitVal = pr.waitFor();
System.out.println("Exited with error code "+exitVal);
} catch(Exception e) {
System.out.println(e.toString());
e.printStackTrace();
}
The problem is the output of the second command ("whoami") doesn't display the current user which used on the first command ("su - test")!
Is there any problem on this code please?

In the general case, you need to run the commands in a shell. Something like this:
Process pr = rt.exec(new String[]{"/bin/sh", "-c", "cd /tmp ; ls"});
But in this case that's not going to work, because su is itself creating an interactive subshell. You can do this though:
Process pr = rt.exec(new String[]{"su", "-c", "whoami", "-", "test"});
or
Process pr = rt.exec(new String[]{"su", "test", "-c", "whoami"});
Another alternative is to use sudo instead of su; e.g.
Process pr = rt.exec(new String[]{"sudo", "-u", "test", "whoami"});
Note: while none of the above actually require this, it is a good idea to assemble the "command line" as an array of Strings, rather than getting exec to do the "parsing". (The problem is that execs splitter does not understand shell quoting.)

As stated in the Javadoc for Runtime.exec():
Executes the specified string command in a separate process.
each time you execute a command via exec() it will be executed in a separate subprocess. This also means that the effect of su ceases to exist immediately upon return, and that's why the whoami command will be executed in another subprocess, again using the user that initially launched the program.
su test -c whoami
will give you the result you want.

If you want to run multiple commands in a way the commands would execute in a subshell if need be see the response here
How can I run multiple commands in just one cmd windows in Java? (using ProcessBuilder to simulate a shell)

Java throws Process exitValue: 127 when running expect script

I'm trying a new approach to a hitch I've been stuck on. Instead of using expect4j for my SSH connection, (I couldn't figure out a way past blocking consumer runs and issues with closures, see past posts for more info on that if you're knowledgeable and feeling saintly,) I'm going to try to use an expect script. I have a runtime exec coded in to a button.onclick, see below. Why am I getting a 127 exit value? I basically just need this expect script to ssh in, run a single set of expect and send, give me the readout, and that's it...
I'm using cygwin. Not sure if that's relevant to why this isn't working...is my sh-bang line pointing to the right place? My cygwin install is a full install, all packages, in C:\cygwin.
Why am I getting a 127 exit value instead of a readout from my server, and how do I alleviate this?
try
{
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec( new String [] {"C:\\cygwin\\bin\\bash.exe", "C:\\scripts\\login.exp"});
InputStream stdin = proc.getInputStream();
InputStreamReader isr = new InputStreamReader(stdin);
BufferedReader br = new BufferedReader(isr);
String line = null;
System.out.println("<OUTPUT>");
while ( (line = br.readLine()) != null)
System.out.println(line);
System.out.println("</OUTPUT>");
int exitVal = proc.waitFor();
System.out.println("Process exitValue: " + exitVal);
} catch (Throwable t)
{
t.printStackTrace();
}
#!/usr/bin/expect -f
spawn ssh userid#xxx.xxx.xxx.xxx password
match_max 100000
expect "/r/nDestination: "
send -- "xxxxxx\r"
expect eof

The problem is that you use bash to execute an expect script. You need to use expect to execute an expect script, or bash to execute an expect script by means of a shell commandline (that would be Process proc = rt.exec( new String [] {"C:\\cygwin\\bin\\bash.exe", "-c", "C:\\scripts\\login.exp"});, note the "-c" which I have inserted) which makes use of the magic shebang at the top of your script. Or better, use only the shebang: Process proc = rt.exec( new String [] {"C:\\scripts\\login.exp"});
The exit value of 127 is a special exit value, and tells you "command not found". Which makes sense as you expect script contains many words for which no system binaries or shell builtins exist.

External process launched with ProcessBuilder/Runtime.exec() fails on XP, works on Win 7

I am working on a Java program that has to fetch the machine serial number, CPU serial number etc. On Windows, the WMI interface is the best way to query for such information, and the standard way to query using the commandline is
wmic bios get serialnumber
which produces output:
SerialNumber
WWV46RT609A3467173E
Translating this into Java, I have used both Runtime.exec() and a ProcessBuilder like so:
(The commented Process p is what I did previously). Here, component and item correspond to 'bios' and 'serialnumber' in the commandline above.
String ret = "";
ProcessBuilder pb = new ProcessBuilder("wmic", component, "get", item);
pb.redirectErrorStream(true);
// Process p = Runtime.getRuntime().exec(
// "wmic " + component + " get " + item);
Process p = pb.start();
InputStreamReader isr = new InputStreamReader(p.getInputStream());
BufferedReader input = new BufferedReader(isr);
String str;
while ((str = input.readLine()) != null) {
if (str.equalsIgnoreCase(item) || StringUtils.isBlank(str)) {
continue;
}
ret = str.trim();
}
input.close();
isr.close();
System.out.println(ret);
This snippet works perfectly on Windows 7, but hangs on Windows XP. Using wmic from the commandline works on both OSes.
I read here that there's a problem with handling both stdout and stderr of the called process, hence the redirectErrorStream() call.
Why does it work flawlessly on Windows 7 but fail on XP? Is there a way other than spawning a separate thread, aka 'StreamGobbler'? (The linked example is quite ancient, and predates the ProcessBuilder class, with its redirectErrorStream() call.

I hope that you have by now got a resolution to this issue. If not, this is what you need to do. First, I also encountered with the same issues and came to discover that it is bufferedReader issue. It is gets into a deadlock situation that resulting into windows xp hanging. The solution is to simulate the end of line (eof) to the bufferedreader by appending "<NUL" the the command.
String[] command = {"CMD", "/C", "WMIC COMPUTERSYSTEM GET USERNAME <NUL "} and executing this command.

You have to use threads to capture ouputs (standard & error).
You can also take a look at this Apache library.

running Echo from Java

I'm trying out the Runtime.exec() method to run a command line process.
I wrote this sample code, which runs without problems but doesn't produce a file at c:\tmp.txt.
String cmdLine = "echo foo > c:\\tmp.txt";
Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(cmdLine);
BufferedReader input = new BufferedReader(
new InputStreamReader(pr.getInputStream()));
String line;
StringBuilder output = new StringBuilder();
while ((line = input.readLine()) != null) {
output.append(line);
}
int exitVal = pr.waitFor();
logger.info(String.format("Ran command '%s', got exit code %d, output:\n%s", cmdLine, exitVal, output));
The output is
INFO 21-04 20:02:03,024 - Ran command
'echo foo > c:\tmp.txt', got exit code
0, output: foo > c:\tmp.txt

echo is not a standalone command under Windows, but embedded in cmd.exe.
I believe you need to invoke a command like "cmd.exe /C echo ...".

The > is intrepreted by the shell, when echo is run in the cmmand line, and it's the shell who create the file.
When you use it from Java, there is no shell, and what the command sees as argument is :
"foo > c:\tmp.txt"
( Which you can confirm, from the execution output )

You can't just pass "> c:\tmp.txt" to Runtime.exec as part of the command line to make redirection happen. From the Javadocs: "All its standard io (i.e. stdin, stdout, stderr) operations will be redirected to the parent process through three streams (getOutputStream(), getInputStream(), getErrorStream())."
If you want to redirect output to a file, to the best of my knowledge the only way to do that would be to open the file in Java, do getInputStream, and then read from the process's input stream and write to the desired file.