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Daniel Kaplan
Asked: 2021-01-13 08:18:28 +0800 CST

I can launch a Perl script with cron, but can I make it open up a window?

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I have an Perl script that runs all night, through a terminal window (Win10 putty.exe) on my Ubuntu server. As with many home networks, I occasionally lose my internet connection, which kills my connection and the script.

Running another Perl script through cron (which checks if my script is running), I am able to restart the Perl script.

However it is running without a window.

Is there a method that when I putty into Ubuntu, I can open a terminal window that shows the output from my Perl script which is now running?

Thank you.

command-line

2 Answers

  1. Best Answer

    You can redirect the output from the cron script to a file >> /path/filename.log

    Or start the script with screen: screen -Sdm perl /path/to/script.pl

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  2. Run the script in screen, ie. before you start the script, type screen (if you get "command not found", you need first to install the screen package). It will just display system prompt as if nothing has changed, but since now you got a virtual terminal that survives loss of your connection. Script will continue to run in that terminal even when you disconnect.

    When you lose connection, after reconnecting to your server, type screen -ls. This will list your screen sessions. The output can look like this:

    There is a screen on:
    19923.pts-10.myserver   (Detached)
1 Socket in /var/run/screen/S-myuser.

    ("myserver" and "myuser" will be your actual hostname and username respectively). If you see "Detached" as above, it means that server correctly noticed that connection was lost and the session has been properly disconnected. In that case, you can reattach to that session with the command:

    screen -r 19923

    where of course the number 19923 is the PID of the screen process that you got from the screen -ls command.

    However, it might be that the server did not notice disconnection and your screen session is still "Attached" to the session that no longer exists. In that case you need first disconnect your screen session before re-attaching to it, you can do this by specifying additionally the -d parameter:

    screen -d -r 19923

    That is a commonly used and de facto standard solution for running programs that should be protected from accidental closing of terminal session and continue to run even if that happens.

    When your script finishes and returns to OS, then first exit command typed at the OS prompt will termninate screen and return you back to regular terminal session (you will see a message "screen is terminating"). The second exit command will log you out.

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