Question

I am working on a Java Project for my own learning, what i have made is a class which can both read and write to external process using Runtime.getRuntime().exec(cmd);

Now i was wondering is there any special way of checking if a particular software/tool is installed on the system.

Like i use sshpass utility to remotely login to other machines, and if it is not there already i would like to install it using my program. But for this how should i go about checking if it exists there or not?

The idea i have in my mind is to run the command and see the response, if the returned string matches particular expression based on that i would decide it’s existence or non-existence.

Do you think it is the right approach or is there any other way to find out this?

Like on windows, i think there are cmdline utilities like ftype, assoc etc,
thank you,

Answer 1

If you already know the name of the software binary (which is usually the same to process name) you can use which command.

You can test it in bash/shell
which firefox
/usr/bin/firefox

Also I can supply you an example written in C# of bash output reading:

string output = string.Empty;

string output = string.Empty;

try
{
    // Sets up our process, the first argument is the command
    // and the second holds the arguments passed to the command
    ProcessStartInfo ps = new ProcessStartInfo("bash");
    ps.Arguments = "-c 'firefox'";
    ps.UseShellExecute = false;

    // Redirects the standard output so it reads internally in out program
    ps.RedirectStandardOutput = true;

    // Starts the process
    using (Process p = Process.Start(ps))
    {
        // Reads the output to a string
        output = p.StandardOutput.ReadToEnd();

        // Waits for the process to exit must come *after* StandardOutput is "empty"
        // so that we don't deadlock because the intermediate kernel pipe is full.
        p.WaitForExit();
    }
}
catch
{
    // TODO manage errors
}

If the bash output is multi-line you can pre-filter it by piping to the grep command:

ps.Arguments = "-c 'cpuid | grep MySearchTerm'";

EDIT 1: Reply to comments

The major problem is the software installation, which requires “administrative” rights.
I’ve tried to create a workaround, but the following line breaks all code:

process = Runtime.getRuntime().exec(new String[]{"/bin/bash","-c","'echo RIadminXsrv1 | sudo -S apt-get install telnet -qy'"});

While in terminal the following command will actually attempt to install telnet (you might have to insert your user into /etc/sudoers to reproduce it on your PC).

/bin/echo myUserPass | /usr/bin/sudo -S /usr/bin/apt-get install telnet -qy

In java it will simply print (echo output) the remaining part of the command:

myUserPass | /usr/bin/sudo -S /usr/bin/apt-get install telnet -qy

This happens because we are simply executing /bin/echo command with a lot of parameters.
I thought that it is possible to actually run the entire set of commands using bash:

bash -c '/bin/echo myUserPass | /usr/bin/sudo -S /usr/bin/apt-get install telnet -qy'

..but it’s not, because bash -c '..' in Java doesn’t work like it should. It says that -c ‘echo …’ script file can not be found, so I suppose that it misinterprets -c option.
BTW I have never had this kind of problem in Mono C#.

Here is the entire snippet:

package javaapplication1;

import java.io.*;

public class JavaApplication1 {

    public static void main(String[] args) {

        Process process;
        String softwareToCheck = "telnet"; // Change here

        try
        {       
            if(!_softwareExists(softwareToCheck))
            {
                System.out.println("Installing missing software..");
                process = Runtime.getRuntime().exec(new String[]{"/bin/bash","-c","'echo RIadminXsrv1 | sudo -S apt-get install telnet -qy'"});

                try
                {
                    process.waitFor();
                }
                catch(InterruptedException e)
                {
                    System.out.println(e.getMessage());
                }

                if(!_softwareExists(softwareToCheck))
                {
                    System.out.println("Software is still missing!");
                }

            }
            else
            {
                System.out.println("Software is installed!");
            }
        }
        catch(IOException e)
        {
            System.out.println(e.getMessage());
        }        
    }

    private static boolean _softwareExists(String binaryName) throws IOException
    {
        String line;
        ProcessBuilder builder;
        BufferedReader reader;
        Process process;

        builder = new ProcessBuilder("/usr/bin/which", binaryName);
        builder.redirectErrorStream(true);
        process = builder.start();
        reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
        try
        {
            process.waitFor();
        }
        catch(InterruptedException e) {
            System.out.println(e.getMessage());
        }

        while ((line = reader.readLine ()) != null)
        {
            break; // Reads only the first line
        }

        return (line != null && !line.isEmpty());

    }
}