Search file on SSH server for a pattern (with less command) using JSch

Question

I am currently trying to access a Linux server and run some commands. The general idea is to search for a log file containing certain text and then access that log, search for the requisite text and store all the data currently displayed on the screen in a String.

This approach works fine through PuTTY but now the requirement is different.

I have accomplished this task on other commands like ls and other commands that provide a direct output. However, I am having no luck with commands like less or more.

I have of course tried on sending the entire contents of the log to an array list and then searching for my text (seeing as I will have a relative idea of the position of the data once the 1st line is found). However, this takes a huge amount of time as the log size varies from 10 Mb to 750 Mb.

I would appreciate if anyone can think of another approach or provide any ideas towards a feasible way to this approach.

For reference: Code I have tried

public class check {

private Session session;

private String username = "user";
private String password = "pass";
private String hostname = "host";

public SSHConnectionManager() 
{ }

public SSHConnectionManager(String hostname, String username, String password) 
{
    this.hostname = hostname;
    this.username = username;
    this.password = password;
}

public void open() throws JSchException 
{
    open(this.hostname, this.username, this.password);
}

public void open(String hostname, String username, String password) throws JSchException
{

    JSch jSch = new JSch();

    session = jSch.getSession(username, hostname, 22);
    Properties config = new Properties(); 
    config.put("StrictHostKeyChecking", "no");  // not recommended
    session.setConfig(config);
    session.setPassword(password);

    System.out.println("Connecting SSH to " + hostname + " - Please wait for few seconds... ");
    session.connect();
    System.out.println("Connected!");
}

public String runCommand(String command) throws JSchException, IOException 
{

    String ret = "";

    if (!session.isConnected())
        throw new RuntimeException("Not connected to an open session.  Call open() first!");

    ChannelExec channel = null;
    channel = (ChannelExec) session.openChannel("exec");

    channel.setCommand(command);
    channel.setInputStream(null);

    PrintStream out = new PrintStream(channel.getOutputStream());
    InputStream in = channel.getInputStream(); // channel.getInputStream();

    channel.connect();

    ret = getChannelOutput(channel, in);

    channel.disconnect();

    System.out.println("Finished sending commands!");

    return ret;
}


private String getChannelOutput(Channel channel, InputStream in) throws IOException
{

    byte[] buffer = new byte[1024];
    StringBuilder strBuilder = new StringBuilder();

    String line = "";
    while (true){
        while (in.available() > 0) {
            int i = in.read(buffer, 0, 1024);
            if (i < 0) {
                break;
            }
            strBuilder.append(new String(buffer, 0, i));
            System.out.println(line);
        }

        if(line.contains("logout")){
            break;
        }

        if (channel.isClosed()){
            break;
        }
        try {
            Thread.sleep(1000);
        } catch (Exception ee){}
    }

    return strBuilder.toString();   
}

public void close()
{        
    session.disconnect();
    System.out.println("Disconnected channel and session");
}


public static void main(String[] args)
{

    SSHConnectionManager ssh = new SSHConnectionManager();
    try {
        ssh.open();
        String ret = ssh.runCommand("ls -l");
        System.out.println(ret);
        ret=ssh.runCommand("cd *move to path of log*");
        System.out.println(ret);
        ret=ssh.runCommand("less *log name*");
        System.out.println(ret);
        ret=ssh.runCommand("/*searchtext*");
        System.out.println(ret);


        ssh.close();

        } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        }
    }
}

I get the necesaary output for my ls command but not for any of the others.

score 1 · Accepted Answer · answered Apr 09 '18 at 14:08

First, your code executes every command in its own separate shell. So the cd command has no effect on the less command. Send, /*searchtext* is not a command at all. Note that setCommand is not an equivalent of typing something in SSH console window. It's completely different interface.

First step would be to execute all commands in the same shell. For that use a shell technique of your server. On Linux server, you would use semicolon or double ampersand. As for example shown here: Multiple commands using JSch.

Though it won't help you with the /*searchtext*. You should not try to use "human" techniques for automation.

In the end, the better solution is to actually do everything with a single command, like using grep:

grep *searchtext* *move to path of log*/*log name*

Search file on SSH server for a pattern (with less command) using JSch

1 Answers1