[SOLVED] Using GNU Screen completely transparently and automatically

Issue

Screen is amazing, of course, but I don't want to have to think about it. I often ssh to a machine, start doing a bunch of stuff, and then think "gosh, I wish I had thought to start a screen session before doing all that so I could reconnect to this from home later".

I'd like to have screen automatically started whenever I log in to a machine. And when I get disconnected, I want to be able to immediately and simply reconnect without fussing with "screen -ls" and "screen -dr".

I have a script that implements one solution to this problem which I'll post as an answer. I'm interested to see other approaches.

Solution

Use the following, ssc, instead of ssh. If you just do "ssc remote.com" then it will list existing screen sessions. Give it a 3rd argument and it will connect to that screen session, or create it and connect to it. Either way, if you get disconnected you can just do "up-arrow, enter" in the shell to reconnect. Zero knowledge of screen required! Edit: Thanks to @klochner for extending this to handle arbitrary ssh options. You can now use this just like ssh!

#!/usr/bin/env perl
# Use 'ssc' (this script) instead of 'ssh' to log into a remote machine.
# Without an argument after the hostname it will list available screens.
# Add an argument after the hostname to attach to an existing screen, or
#   specify a new screen.  Eg, ssc remote.com foo
# The numbers in front of the screen tag can usually be ignored.

# ssh option parsing by @klochner
my $optstring = ""; 
while ($val = shift) {
  if    ($val =~ /^-\w$/)  { $optstring .= " ".$val.(shift); }
  elsif ($val =~ /^-\w+$/) { $optstring .= " ".$val;         }
  elsif ($machine)         { $tag        =     $val;         }
  else                     { $machine    =     $val;         }
}

if (!$machine) {
  print "USAGE: ssc [ssh options] remote.com [screen name]\n";
} elsif (!$tag) {
  @screens = split("\n", `ssh $optstring $machine screen -ls`);
  for(@screens) {
    if(/^\s*(\d+)\.(\S+)\s+\(([^\)]*)\)/) {
      ($num, $tag, $status) = ($1, $2, $3);
      if($status =~ /attached/i) { $att{"$num.$tag"} = 1; }
      elsif($status =~ /detached/i) { $att{"$num.$tag"} = 0; }
      else { print "Couldn't parse this: $_\n"; }
      # remember anything weird about the screen, like shared screens
      if($status =~ /^(attached|detached)$/i) { 
        $special{"$num.$tag"} = "";
      } else {
        $special{"$num.$tag"} = "[$status]";
      }
    }
  }
  print "ATTACHED:\n";
  for(sort { ($a=~/\.(\w+)/)[0] cmp ($b=~/\.(\w+)/)[0] } keys(%att)) {
    ($tag) = /\.(\w+)/;
    print "  $tag\t($_)\t$special{$_}\n" if $att{$_};
  }
  print "DETACHED:\n";
  for(sort { ($a=~/\.(\w+)/)[0] cmp ($b=~/\.(\w+)/)[0] } keys(%att)) {
    ($tag) = /\.(\w+)/;
    print "  $tag\t($_)\t$special{$_}\n" unless $att{$_};
  }
} else {
 system("ssh $optstring -t $machine \"screen -S $tag -dr || screen -S $tag\"");
}

Btw, there's a trick to forcing an ssh session to exit and give you back your local terminal prompt when you lose network connectivity:
https://superuser.com/questions/147873/ssh-sessions-in-xterms-freeze-for-many-minutes-whenever-they-disconnect

Answered By - dreeves

Answer Checked By - Senaida (WPSolving Volunteer)