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Junit5 is unable to execute shell commands within tests

I had question about running scripts using Junit 5. I have the following piece of code:
public class RunMvnSubprocess {
#Test
public void main() throws IOException, InterruptedException {
String[] cmd = new String[]{"mvn.cmd", "-version"}; // command to be executed on command prompt.
Process p = Runtime.getRuntime().exec(cmd);
try (BufferedReader output = new BufferedReader(new InputStreamReader(p.getInputStream()))) {
String line;
while ((line = output.readLine()) != null) {
System.out.println(line);
}
}
p.waitFor();
}
}
I get no output when I run it using Junit 5.7.0. However, running this on Junit 4.13.2 works fine.
Please note that I am running this piece of test in Windows 10 Pro version 21H1.
EDIT:
Modifying
new String[]{"mvn.cmd", "-version"}
to
new String[]{"cmd", "/c", "\"mvn -version\""}
works for me, but launching a subshell is a bad practice so I am keeping this workaround as a last resort.

Note that you are implicity running a sub-shell as the Windows command CMD.EXE is called to interpret the contents of mvn.cmd, so your value of cmd is equivalent to:
cmd = new String[]{ "cmd", "/c", "call mvn.cmd -version"};
If you get no error code from waitFor or no output or no exception, then the issue will be reported in the STDERR stream. Change to use ProcessBuilder instead and you can merge STDERR to STDOUT as follows:
ProcessBuilder pb = new ProcessBuilder(cmd);
// No STDERR => merge to STDOUT
pb.redirectErrorStream(true);
Process p = pb.start();
Also, no need to write much code to consume STDOUT:
try(var stdo = p.getInputStream()) {
stdo.transferTo(System.out);
}
int rc = p.waitFor();
if (rc != 0) throw new RuntimeException("test failed");
Hopefully this will explain your problem with the mvn command.

Excute bash script "ps aux | wc -l" in java response empty result [duplicate]

Consider the following code:
String commandf = "ls /etc | grep release";
try {
// Execute the command and wait for it to complete
Process child = Runtime.getRuntime().exec(commandf);
child.waitFor();
// Print the first 16 bytes of its output
InputStream i = child.getInputStream();
byte[] b = new byte[16];
i.read(b, 0, b.length);
System.out.println(new String(b));
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
The program's output is:
/etc:
adduser.co
When I run from the shell, of course, it works as expected:
poundifdef#parker:~/rabbit_test$ ls /etc | grep release
lsb-release
The internets tell me that, due to the fact that pipe behavior isn't cross-platform, the brilliant minds who work in the Java factory producing Java can't guarantee that pipes work.
How can I do this?
I am not going to do all of my parsing using Java constructs rather than grep and sed, because if I want to change the language, I'll be forced to re-write my parsing code in that language, which is totally a no-go.
How can I make Java do piping and redirection when calling shell commands?

Write a script, and execute the script instead of separate commands.
Pipe is a part of the shell, so you can also do something like this:
String[] cmd = {
"/bin/sh",
"-c",
"ls /etc | grep release"
};
Process p = Runtime.getRuntime().exec(cmd);

I ran into a similar problem in Linux, except it was "ps -ef | grep someprocess".
At least with "ls" you have a language-independent (albeit slower) Java replacement. Eg.:
File f = new File("C:\\");
String[] files = f.listFiles(new File("/home/tihamer"));
for (String file : files) {
if (file.matches(.*some.*)) { System.out.println(file); }
}
With "ps", it's a bit harder, because Java doesn't seem to have an API for it.
I've heard that Sigar might be able to help us:
https://support.hyperic.com/display/SIGAR/Home
The simplest solution, however, (as pointed out by Kaj) is to execute the piped command as a string array. Here is the full code:
try {
String line;
String[] cmd = { "/bin/sh", "-c", "ps -ef | grep export" };
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader in =
new BufferedReader(new InputStreamReader(p.getInputStream()));
while ((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
} catch (Exception ex) {
ex.printStackTrace();
}
As to why the String array works with pipe, while a single string does not... it's one of the mysteries of the universe (especially if you haven't read the source code). I suspect that it's because when exec is given a single string, it parses it first (in a way that we don't like). In contrast, when exec is given a string array, it simply passes it on to the operating system without parsing it.
Actually, if we take time out of busy day and look at the source code
(at http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/lang/Runtime.java#Runtime.exec%28java.lang.String%2Cjava.lang.String[]%2Cjava.io.File%29), we find that is exactly what is happening:
public Process [More ...] exec(String command, String[] envp, File dir)
throws IOException {
if (command.length() == 0)
throw new IllegalArgumentException("Empty command");
StringTokenizer st = new StringTokenizer(command);
String[] cmdarray = new String[st.countTokens()];
for (int i = 0; st.hasMoreTokens(); i++)
cmdarray[i] = st.nextToken();
return exec(cmdarray, envp, dir);
}

Create a Runtime to run each of the process. Get the OutputStream from the first Runtime and copy it into the InputStream from the second one.

#Kaj accepted answer is for linux. This is the equivalent one for Windows:
String[] cmd = {
"cmd",
"/C",
"dir /B | findstr /R /C:"release""
};
Process p = Runtime.getRuntime().exec(cmd);

One does not simply grep into ProcessBuilder

does anyone know how to use linux grep with the java ProcessBuilder? Why does this code return an empty string when it should return "sing" ?
import java.io.*;
import java.util.*;
public class Test2 {
public static void main(String[] args) throws InterruptedException,IOException{
String line;
// Initiate grep process.
ProcessBuilder pb = new ProcessBuilder("grep", "\"sing\"", "<<<\"sing\"");
Process p = pb.start();
p.waitFor();
// Get grep output:
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
StringBuilder builder = new StringBuilder();
line = null;
while ( (line = reader.readLine()) != null) {
builder.append(line);
builder.append(System.getProperty("line.separator"));
}
String result = builder.toString();
System.out.println(result);
}
}
I also try to echo what I execute with this code:
ProcessBuilder pb = new ProcessBuilder("echo","grep", "\"sing\"", "<<<\"sing\"");
and get the correct result:
grep "sing" <<<"sing"
I finally try to execute the command at the shell and get:
sing
although it is in red font for some reason. So what am I doing wrong?

what am I doing wrong?
Something which is pretty obvious.
Do you expect, say, execve(), to understand shell constructs? No.
Well, you shouldn't be expecting ProcessBuilder to understand those either. Although it is not as low level as execve(), it is low level enough that the arguments to a command are "raw". Therefore, in your command, <<<"sing" is passed as is as an argument to grep; which means grep views it as a file to read from.
Get that in your head: what you type in the shell is interpreted by the shell; a ProcessBuilder WILL NOT use a shell to execute its processes, nor will execve(). Which, in turn, means that you cannot use shell constructs.
If you want to grep you'll have to feed your process' input with the text you want. But why use grep when Java has a builtin regex engine is another question, of course.
As to:
although it is in red font for some reason
it is simply text decoration from the grep command (well, GNU grep at least); see its manpage and the --color option. In short, in your case, it has detected that your tty had the capabilities to change the color of text and it uses that to decorate the matched text.
Try and:
echo foobar | grep foo
It will echo foobar with foo in red.

You can actually run the same command using ProcessBuilder but you have to make sure it is execute by bash. I prefer this utility method:
public static int runCmd(final String command) {
Process process=null;
int ret = 0;
String[] finalCommand = new String[] { "bash", "-c", command };
try {
final ProcessBuilder processBuilder = new ProcessBuilder(finalCommand);
processBuilder.redirectErrorStream(true);
process = processBuilder.start();
ret = process.waitFor();
// stdout+stderr
InputStreamReader isr = new InputStreamReader( process.getInputStream() );
BufferedReader br = new BufferedReader(isr);
String line;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
//System.out.println("Program terminated!");
process.destroy();
br.close();
isr.close();
}
catch (IOException|InterruptedException e) {
e.printStackTrace();
}
return ret;
}
Then call it as:
runCmd("grep -o \"sing\" <<<\"icansing\"");
And it gives me this output:
sing

How to make pipes work with Runtime.exec()?

Consider the following code:
String commandf = "ls /etc | grep release";
try {
// Execute the command and wait for it to complete
Process child = Runtime.getRuntime().exec(commandf);
child.waitFor();
// Print the first 16 bytes of its output
InputStream i = child.getInputStream();
byte[] b = new byte[16];
i.read(b, 0, b.length);
System.out.println(new String(b));
} catch (IOException e) {
e.printStackTrace();
System.exit(-1);
}
The program's output is:
/etc:
adduser.co
When I run from the shell, of course, it works as expected:
poundifdef#parker:~/rabbit_test$ ls /etc | grep release
lsb-release
The internets tell me that, due to the fact that pipe behavior isn't cross-platform, the brilliant minds who work in the Java factory producing Java can't guarantee that pipes work.
How can I do this?
I am not going to do all of my parsing using Java constructs rather than grep and sed, because if I want to change the language, I'll be forced to re-write my parsing code in that language, which is totally a no-go.
How can I make Java do piping and redirection when calling shell commands?

Write a script, and execute the script instead of separate commands.
Pipe is a part of the shell, so you can also do something like this:
String[] cmd = {
"/bin/sh",
"-c",
"ls /etc | grep release"
};
Process p = Runtime.getRuntime().exec(cmd);

I ran into a similar problem in Linux, except it was "ps -ef | grep someprocess".
At least with "ls" you have a language-independent (albeit slower) Java replacement. Eg.:
File f = new File("C:\\");
String[] files = f.listFiles(new File("/home/tihamer"));
for (String file : files) {
if (file.matches(.*some.*)) { System.out.println(file); }
}
With "ps", it's a bit harder, because Java doesn't seem to have an API for it.
I've heard that Sigar might be able to help us:
https://support.hyperic.com/display/SIGAR/Home
The simplest solution, however, (as pointed out by Kaj) is to execute the piped command as a string array. Here is the full code:
try {
String line;
String[] cmd = { "/bin/sh", "-c", "ps -ef | grep export" };
Process p = Runtime.getRuntime().exec(cmd);
BufferedReader in =
new BufferedReader(new InputStreamReader(p.getInputStream()));
while ((line = in.readLine()) != null) {
System.out.println(line);
}
in.close();
} catch (Exception ex) {
ex.printStackTrace();
}
As to why the String array works with pipe, while a single string does not... it's one of the mysteries of the universe (especially if you haven't read the source code). I suspect that it's because when exec is given a single string, it parses it first (in a way that we don't like). In contrast, when exec is given a string array, it simply passes it on to the operating system without parsing it.
Actually, if we take time out of busy day and look at the source code
(at http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/lang/Runtime.java#Runtime.exec%28java.lang.String%2Cjava.lang.String[]%2Cjava.io.File%29), we find that is exactly what is happening:
public Process [More ...] exec(String command, String[] envp, File dir)
throws IOException {
if (command.length() == 0)
throw new IllegalArgumentException("Empty command");
StringTokenizer st = new StringTokenizer(command);
String[] cmdarray = new String[st.countTokens()];
for (int i = 0; st.hasMoreTokens(); i++)
cmdarray[i] = st.nextToken();
return exec(cmdarray, envp, dir);
}

Create a Runtime to run each of the process. Get the OutputStream from the first Runtime and copy it into the InputStream from the second one.

#Kaj accepted answer is for linux. This is the equivalent one for Windows:
String[] cmd = {
"cmd",
"/C",
"dir /B | findstr /R /C:"release""
};
Process p = Runtime.getRuntime().exec(cmd);

Printing my Mac's serial number in java using Unix commands

I am trying to print my mac's [edit: Apple computer] serial number in a java program. I am familiar with the Unix command
ioreg -l | awk '/IOPlatformSerialNumber/ { print $4;}'
which accomplishes this task in terminal.
When I try
String command = "ioreg -l | awk '/IOPlatformSerialNumber/ { print $4; }'"
Runtime terminal = Runtime.getRuntime();
String input = new BufferedReader(
new InputStreamReader(
terminal.exec(commands).getInputStream())).readLine();
System.out.println(new BufferedReader(
new InputStreamReader(
terminal.exec(command, args).getInputStream())).readLine());
my serial number is not printed. Instead it prints:
<+-o Root class IORegistryEntry, id 0x100000100, retain 10>
I think the problem is that terminal.exec() is not meant to take the whole command string. Is there something in java similar to the argument shell = True in python's Popen(command, stdout=PIPE, shell=True) that will allow me to pass the whole command string?

I see two possibilities:
Parse the output of ioreg -l using, say, Scanner.
Wrap the command in a shell script and exec() it:
#!/bin/sh
ioreg -l | awk '/IOPlatformSerialNumber/ { print $4;}'
Addendum: As an example of using ProcessBuilder, and incorporating a helpful suggestion by Paul Cager, here's a third alternative:
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class PBTest {
public static void main(String[] args) {
ProcessBuilder pb = new ProcessBuilder("bash", "-c",
"ioreg -l | awk '/IOPlatformSerialNumber/ { print $4;}'");
pb.redirectErrorStream(true);
try {
Process p = pb.start();
String s;
// read from the process's combined stdout & stderr
BufferedReader stdout = new BufferedReader(
new InputStreamReader(p.getInputStream()));
while ((s = stdout.readLine()) != null) {
System.out.println(s);
}
System.out.println("Exit value: " + p.waitFor());
p.getInputStream().close();
p.getOutputStream().close();
p.getErrorStream().close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}

Pipes aren't supported by Runtime.exec(..) since they are a feature of shells. Instead, you'd have to emulate the pipe yourself, e.g.
String ioreg = toString(Runtime.exec("ioreg -l ").getInputStream());
Process awk = Runtime.exec("awk '/IOPlatformSerialNumber/ { print $4;}'");
write(awk.getOutputStream(), ioreg);
String input = new BufferedReader(new InputStreamReader(awk.getInputStream())).readLine();
Alternatively, you could of course run a shell as a process, e.g. Runtime.exec("bash"), and interact with it by reading and writing its IO streams. Interacting with processes is a bit tricky though and has some gotchas and let it execute your command (see comments)

To get the MAC addres via Java you can use java.net.NetworkInterface:
NetworkInterface.getByName("xxx").getHardwareAddress()
If you don't know the name (I assume it to be 'eth0' on linux) of your network interface, you can even iterate throug all of your network interfaces using NetworkInterface.getNetworkInterfaces().