Develop Reference

Difference when executing linux command from terminal and java runtime process

I'm looking a way to write running log of python which is executed by java app via script.
Let's say my script is:
import time
for x in range(120):
print("Running ", x)
time.sleep(1)
Here is my current solution:
Trigger script using java
String cmd = "python script.py";
var process = Runtime.getRuntime().exec(cmd, null, new File(sandboxPath));
Write log to new file:
String traceLogCmd = String.format("strace -p %s -s 9999 -e trace=write -o output.txt", process.pid());
Runtime.getRuntime().exec(traceLogCmd, null, new File(sandboxPath));
Now the problem is output.txt only has content whenever the python script is done executing so that I cannot tailf the output file.
Meanwhile if I execute python script.py and strace command dirrectly from terminal, the output is exactly what I expected.
Can someone correct me if I did something wrong or have a another way to get python log?
Thanks in advance.

Use ProcessBuilder instead of Runtime.exec(). More details: When Runtime.exec() won't
The following code will append to StringBuilder object output of the script sb.append(line);. It would not be difficult to write that content to a file.
Process p = new ProcessBuilder("sh", "-c", "python", "path-to-your-script").start();
String result = getCommandResult(p.getInputStream());
private static String getCommandResult(InputStream stream) throws IOException {
StringBuilder sb = new StringBuilder();
try (InputStreamReader isr = new InputStreamReader(stream);
BufferedReader in = new BufferedReader(isr)) {
String line;
while ((line = in.readLine()) != null) {
sb.append(line);
}
}
return sb.toString().trim();
}

Run shell script from java

I have sendmail file that contains this script echo "sample message" | /usr/bin/swaks --to email#gmail.com I want to run it from java using this code :
ProcessBuilder pb = new ProcessBuilder("sendmail");
Process p = pb.start()
but the email is not sent. Whats wrong and how can i fix this?
edit : running ./sendmail is working, and the email is sent to my mail

I think the problem is that your java application is ending before the script finishes.
Try this:
ProcessBuilder pb = new ProcessBuilder("./sendmail.sh");
Process p = pb.start();
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
String readline;
int i = 0;
while ((readline = reader.readLine()) != null) {
System.out.println(++i + " " + readline);
}
The above code should print out what your command prints which could help you debug. It also has the side effect of blocking until the script is finished.
If that works and you don't care about the output, you can do this:
ProcessBuilder pb = new ProcessBuilder("./test.sh");
Process p = pb.start();
p.waitFor();

How to execute Python script from Java (via command line)?

I can execute Linux commands like ls or pwd from Java without problems but couldn't get a Python script executed.
This is my code:
Process p;
try{
System.out.println("SEND");
String cmd = "/bash/bin -c echo password| python script.py '" + packet.toString() + "'";
//System.out.println(cmd);
p = Runtime.getRuntime().exec(cmd);
BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
String s = br.readLine();
System.out.println(s);
System.out.println("Sent");
p.waitFor();
p.destroy();
} catch (Exception e) {}
Nothing happened. It reached SEND but it just stopped after it...
I am trying to execute a script which needs root permissions because it uses serial port. Also, I have to pass a string with some parameters (packet).

You cannot use the PIPE inside the Runtime.getRuntime().exec() as you do in your example. PIPE is part of the shell.
You could do either
Put your command to a shell script and execute that shell script with .exec() or
You can do something similar to the following
String[] cmd = {
"/bin/bash",
"-c",
"echo password | python script.py '" + packet.toString() + "'"
};
Runtime.getRuntime().exec(cmd);

#Alper's answer should work. Better yet, though, don't use a shell script and redirection at all. You can write the password directly to the process' stdin using the (confusingly named) Process.getOutputStream().
Process p = Runtime.exec(
new String[]{"python", "script.py", packet.toString()});
BufferedWriter writer = new BufferedWriter(
new OutputStreamWriter(p.getOutputStream()));
writer.write("password");
writer.newLine();
writer.close();

You would do worse than to try embedding jython and executing your script. A simple example should help:
ScriptEngine engine = new ScriptEngineManager().getEngineByName("python");
// Using the eval() method on the engine causes a direct
// interpretataion and execution of the code string passed into it
engine.eval("import sys");
engine.eval("print sys");
If you need further help, leave a comment. This does not create an additional process.

First, open terminal and type "which python3". You will get the complete path of python3. For example "/usr/local/bin/python3"
String[] cmd = {"/usr/local/bin/python3", "arg1", "arg2"};
Process p = Runtime.getRuntime().exec(cmd);
p.waitFor();
String line = "", output = "";
StringBuilder sb = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
while ((line = br.readLine())!= null) {sb = sb.append(line).append("\n"); }
output = sb.toString();
System.out.println(output);

How to edit file on console from Java?

I'm trying to edit a file from CLI. I'm executing the nano command (I know that command will always be available); when I execute it, I can see nano's output but I cannot interact with it. How can I pass user input to the command? Do you have a better idea to easily edit a file from within my Java app?
This is my code:
String command = "nano /tmp/163377867.txt ";
try {
Process process = Runtime.getRuntime().exec(command);
InputStream inputStream = process.getInputStream();
InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String line;
while ((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}

The problem with Java's Runtime.exec is that it connects stdin and stdout to "pipes," while many console programs need a TTY device.
One way to solve this problem is to make the Java program's controlling terminal available to the program you execute:
Process proc = Runtime.getRuntime().exec(new String[]{
"sh", "-c", command+" </dev/tty >/dev/tty"});
proc.waitFor(); // wait for user to finish editing the file

Running Python scripts in Java

I'm trying to run a python script during the execution of my java code, because it will depend on the output received from the python script. So far I've tried using jythonc, unfortunately to no success, and now im trying to use the java Runtime and java Process to execute the python script.
Now I've run into a problem when trying to call the python script. I feel as though it doesn't even call the script because it takes less than a couple seconds to get to the next page....
Could the problem be how I am calling the python script?? I am trying to run this through a web application...
Here is some of my code:
String run = "cmd /c python duplicatetestingoriginal.py" ;
boolean isCreated = fwr.writeFile(BugFile, GD, 500, true, 5, "LET");
if(isCreated){
try{
r = Runtime.getRuntime();
p = r.exec(run);
BufferedReader stdInput = new BufferedReader(new InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new InputStreamReader(p.getErrorStream()));
String line = "";
while ((line = stdInput.readLine()) != null) {
System.out.println(line);
}
while ((line = stdError.readLine()) != null) {
errorW.write(line);
}
int exitVal = p.waitFor();
arrayList = fwr.readResults();
}catch(Exception e){
}
}
else{
// troubleshoot....
}

Instead of String for the command, split it to chunks and make a String[]. No need to state cmd /c, I think.
This is a sample code from my application:
//Running on windows
command = new String[4];
command[0]=directory.getCanonicalPath()+"/data/ExtenalApp.exe"; //extenal commandline app, not placed in path, but in subfolder
command[1]=directory.getCanonicalPath()+"/data/SomeFile.txt"; //file needed for the external app, sent as an argument
command[2]=arg1; //argument for the app
command[3]=arg2; //argument for the app
//Running on Mac
command = new String[6];
command[0]="python";
command[1]=directory.getCanonicalPath()+"/data/wp.py"; //path to the script
command[2]="-F"; //argument/Flag/option
command[3]="--dir="+path; //argument/option
command[4]="--filename="+filename; //argument/option
command[5]=argument; //argument/option
Process process = Runtime.getRuntime().exec(command);
process.waitFor();
process.destroy();
I don't handle the Input/Output streams because the script/app doesn't require input, and outputs only when finished, nothing important. Which might not be the case for you.