Develop Reference

Java Runtime exec() does not resolve environment variable

If I run the following in a terminal I get the expected 123
$ /bin/sh
$ FOO=123
$ echo $FOO
123
Now I try to do the following with Java's Runtime's exec():
String[] envp = { "FOO=123" };
String cmd = "echo $FOO";
Process p = Runtime.getRuntime().exec(cmd, envp);
java.io.BufferedReader reader =
new java.io.BufferedReader(
new java.io.InputStreamReader(p.getInputStream()
)
);
System.out.println(reader.readLine());
I expect to see 123 but instead I get $FOO.
What am I missing?

The following works under Windows.
String[] envp = { "FOO=123" };
String cmd = "cmd /c echo %FOO%";
Process p = Runtime.getRuntime().exec(cmd, envp);
p.waitFor();
java.io.BufferedReader reader =
new java.io.BufferedReader(
new java.io.InputStreamReader(p.getInputStream()
)
);
String line;
while((line = reader.readLine()) != null) {
System.out.println(line);
}

What am I missing?
Firstly,
$ FOO=123
sets a shell variable. It is local to the shell. If you want a variable to be in the environment that child processes see, you must export it.
$ export FOO=123
But that's not the problem.
The real issue is the command string "echo $FOO". The problem is that $FOO is shell syntax .... but when you run a command from Java using exec:
exec itself doesn't understand shell syntax, and
exec doesn't run the command in a shell.
So the parameter that is given to the echo command consists of the literal string $FOO ... and that is what it outputs.
There are three approaches to solving this:
Interpolate the variable in Java; e.g.
String[] cmd = {"echo", "123"};
Process p = Runtime.getRuntime().exec(cmd);
or by doing repeated search / replace for things that look like variables. (But this only deals with environment variable interpolation, not other forms of shell substitution.)
Assuming that you are doing something more complicated than echo, write the command that you are running to do its own interpolation of environment variables. (This is clunky ...)
Explicitly invoke the command in a shell; e.g.
String[] envp = {"FOO=123"};
String[] cmd = {"/bin/sh", "-c", "echo $FOO"};
Process p = Runtime.getRuntime().exec(cmd, envp);
Note that you can use any shell, and provide pretty much any shell-ism that can be expressed in a single shell command line.

Run shell script with Angular CLI commands from Java

I'm trying to run a shell script from Java (using Runtime.getRuntime().exec(cmd)). All commands in the script file seem to be running normally except the angular-cli (ng) commands.
My Java File:
System.out.println("Executing Script...");
final String[] cmd = new String[]{"/bin/bash", "test.sh"};
final Process process = Runtime.getRuntime().exec(cmd);
process.waitFor();
final BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
String s;
while ((s = reader.readLine()) != null) {
System.out.println("Script output: " + s);
}
process.destroy();
System.out.println("Script Executed.");
test.sh:
#!/bin/bash
cd ~/ &&
ng new newAngularProject &&
Outout:
Executing Script...
Script Executed.
No errors are thrown. All other commands work but for some reason, I'm unable to run ng commands. Also, I've tested the file w/o running it from Java - When I run the same script directly on the console, it works perfectly and all commands (including ng commands) work neatly. I'm running on MacOS in case you wanted to know.

Also print the error stream. You will get the error message, if it is there.
final BufferedReader errorReader = new BufferedReader(new InputStreamReader(process.getErrorStream()));
while ((s = errorReader.readLine()) != null) {
System.out.println("error: " + s);
}
Also you can try to use absolute path of ng in your test.sh e.g. /home/my/install/node-vxxx/ng, since the process spawn by java to run your command might not get the environment variable you set in your .bashrc /.bash_aliases

Run exec file using Java on Mac

I need to start a server using bash, so I had created an UNIX shell , but I am not able to execute it with Java from Eclipse.
I tried the following code which doesn't work :
Process proc = Runtime.getRuntime().exec(./startServer);
Here is content of the startServer file :
#!/bin/bash
cd /Users/sujitsoni/Documents/bet/client
npm start

You can try the following two options.
Option 1
Process proc = Runtime.getRuntime().exec("/bin/bash", "-c", "<Abosulte Path>/startServer");
Option 2
ProcessBuilder pb = new ProcessBuilder("/bin/bash", "-c", "<Absolute Path>/startServer");
pb.directory(new File("<Absolute Path>"));
Process proc = pb.start();

A couple Of things can go wrong:
The path to the file you have given might be wrong for eclipse it can take relative path but from the command line, it will take the absolute path.
error=13, Permission denied - If the script file doesn't have required permissions. In your scenario, that might not the case as you are not getting any error.
At last, you are executing the script by java program so the output of your script will not be printed out. In your scenario, this might be the case. You need to capture the output of script from BufferedReade and print it. ( In your case server might have started but you are not seeing the logs/output of the script.
See the code sample below for printing output.
public static void main(String[] args) throws IOException, InterruptedException {
Process proc = Runtime.getRuntime().exec("./startServer");
proc.waitFor();
StringBuffer output = new StringBuffer();
BufferedReader reader = new BufferedReader(new InputStreamReader(proc.getInputStream()));
String line = "";
while ((line = reader.readLine()) != null) {
output.append(line + "\n");
}
System.out.println(output);
}

How to use Java ProcessBuilder to execute ./filename in linux

I'm currently using ProcessBuilder to run some file like test.out.
Here is some of my code
ArrayList cmd = new ArrayList();
cmd.add("sudo");
cmd.add("./test.out");
String s = "";
try{
ProcessBuilder pb = new ProcessBuilder(cmd);
pb.directory(new File("/myPath"));
pb.redircErrorStream(true);
Process p = pb.start();
InputStream is = p.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferReader br = new BufferReader(isr);
String line = "";
while((line = br.readLine()) !=null)
{
s+=line;
}
System.out.println(s);
}
I output the path which is correct("/myPath").
when I remove line
`cmd.add("sudo")`
the output will give me a String:
oneoflib:must be root. Did you forgot sudo?
But once I add
cmd.add("sudo");
there is nothing output.
Is there anyone whats wrong with it?
I can run sudo ./test.out from terminal which works fine.
I'm using eclipse BTW.
Thank you very much.

I guess that getting the error stream from the process could be beneficial here to help debug the problem.
This should help, consider the following bash script and let's call it yourExecutable. Let's also assume that it has all the proper permissions:
if [ "$EUID" -ne 0 ]
then echo "Please run as root"
exit
fi
echo "You are running as root"
When run without sudo it prints "Please run as root" other wise it prints "You are running as root"
The command, ie first argument in your list should be bash, if that is the shell you are using. The first argument should be -c so the commands will be read from the following string. The string should be echo <password> | sudo -S ./yourExecutable. This isn't exactly the best way to send the password to sudo, but I don't think that is the point here. The -S to sudo will prompt for the password which is written to stdout and piped over to sudo.
public static void main(String[] args) throws IOException {
Process process = new ProcessBuilder("bash", "-c", "echo <password> | sudo -S ./yourExecutable").start();
BufferedReader errorReader = new BufferedReader(new InputStreamReader(process.getErrorStream()));
String string;
while((string = errorReader.readLine()) != null){
System.out.println(string);
}
BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
while((string = reader.readLine()) != null){
System.out.println(string);
}
}
Output on my machine looks like:
Password:
You are running as root

Java: Run multiple shell commands?

OK. I've been looking everywhere on how to execute multiple commands on a single command prompt from java. What i need to do is this, but not in command line, in code.
Execute:
cd C:/Android/SDK/platform-tools
adb install superuser.apk
..Basically i want to run adb commands from a program!!! Here is my java code so far:
MainProgram.java
public class MainProgram {
public static void main(String[] args) {
CMD shell = new CMD();
shell.execute("cmd /K cd C:/Android/SDK/platform-tools"); //command 1
shell.execute("cmd /C adb install vending.apk"); // command 2
}
}
CMD.java
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class CMD {
CMD() {
}
// THIS METHOD IS WHERE THE PROBLEM IS
void execute(String command) {
try
{
Process p = Runtime.getRuntime().exec(command);
BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));
// read the output from the command
String s = null;
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
}
catch(Exception e){
e.printStackTrace();
}
}
}
So what happens is...i can run the first command, but that cmd terminates and when i execute the 2nd command, a new cmd is created, hence i get an error because im not in the right directory. I tried a single string command "cmd /C cd C:/blablabla /C adb remount", but that just froze up...
Essentially, command 1 is executed and terminated, then command 2 is executed and terminated. I want it to be like this: command 1 executed, command 2 executed, terminated.
Basically i'm asking how can i run both of these commands in a row on a single command prompt???
My final target is to have a JFrame with a bunch of buttons which execute different adb commands when clicked on.

Easiest way is to make a batch file then call that from program
of course you could just say
C:/Android/SDK/platform-tools/adb install superuser.apk
there's no need to cd to a file if you name it directly
although what you are looking for is already made in ddms.bat which provides a complete visual link to adb

Create file as something.bat and set the contents to:
cd C:/Android/SDK/platform-tools
adb install superuser.apk
Then call:
Process p = Runtime.getRuntime().exec("something.bat");
all commands in the bat file are executed.