Ruby, Run Linux Commands One by One, by Ssh and Log Everything

Ruby, run linux commands one by one, by SSH and LOG everything

Perhaps try it with an ssh channel instead to open a remote shell. That should preserve state between your commands as the connection will be kept open:

http://net-ssh.github.com/ssh/v1/chapter-5.html

Here's also an article of doing something similar with a little bit different approach:

http://drnicwilliams.com/2006/09/22/remote-shell-with-ruby/

Edit 1:

Ok. I see what you are saying. SyncShell was removed from Net::SSH 2.0. However I found this, which looks like it does pretty much what SyncShell did:

http://net-ssh-telnet.rubyforge.org/

Example:

s = Net::SSH.start(host, user)
t = Net::SSH::Telnet.new("Session" => s, "Prompt" => %r{^myprompt :})
puts t.cmd("cd /tmp")  
puts t.cmd("ls")       # <- Lists contents of /tmp

I.e. Net::SSH::Telnet is synchronous, and preserves state, because it runs in a pty with your remote shell environment. Remember to set the correct prompt detection, otherwise Net::SSH::Telnet will appear to hang once you call it (it's trying to find the prompt).

What is the cleanest way to ssh and run multiple commands in Bash?

How about a Bash Here Document:

ssh otherhost << EOF
  ls some_folder; 
  ./someaction.sh 'some params'
  pwd
  ./some_other_action 'other params'
EOF

To avoid the problems mentioned by @Globalz in the comments, you may be able to (depending what you're doing on the remote site) get away with replacing the first line with

ssh otherhost /bin/bash << EOF

Note that you can do variable substitution in the Here document, but you may have to deal with quoting issues. For instance, if you quote the "limit string" (ie. EOF in the above), then you can't do variable substitutions. But without quoting the limit string, variables are substituted. For example, if you have defined $NAME above in your shell script, you could do

ssh otherhost /bin/bash << EOF
touch "/tmp/${NAME}"
EOF

and it would create a file on the destination otherhost with the name of whatever you'd assigned to $NAME. Other rules about shell script quoting also apply, but are too complicated to go into here.

How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`
This is like many other languages, including Bash, PHP, and Perl.
Returns the result (i.e. standard output) of the shell command.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )
Following the x character is a delimiter, which can be any character.
If the delimiter is one of the characters (, [, {, or <,
the literal consists of the characters up to the matching closing delimiter,
taking account of nested delimiter pairs. For all other delimiters, the
literal comprises the characters up to the next occurrence of the
delimiter character. String interpolation #{ ... } is allowed.
Returns the result (i.e. standard output) of the shell command, just like the backticks.
Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system
Executes the given command in a subshell.
Returns true if the command was found and run successfully, false otherwise.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec
Replaces the current process by running the given external command.
Returns none, the current process is replaced and never continues.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice:
$?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}.
You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

http://www.elctech.com/blog/i-m-in-ur-commandline-executin-ma-commands
http://blog.jayfields.com/2006/06/ruby-kernel-system-exec-and-x.html
http://tech.natemurray.com/2007/03/ruby-shell-commands.html

How to run commands while logging from one machine to another using Expect

You want to run the second ssh within the connection you already opened to machine m1, so you don't need a second spawn as this will try to open a new connection from your local machine. So instead of the second spawn, use send to run the ssh command on m1, and then use expect to wait for the prompt on m2 before sending the commands:

send "ssh -X root@$m2"
expect "#"

Ruby and Net::SSH Interfacing with a interactive command line application

After abandoning this for quite some time, I finally found the problem. Obviously just a silly oversight of mine. The problem was in the C program, I simply forgot to flush stdout after writing the command line arguments.
Here's the version that works:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main( int argc, char **argv){
    int i;
    char line[256];
    for (i = 1 ; i < argc ; i++ ){
        printf("arg%d: %s\n", i, argv[i]);
    }

    fflush(stdout); // this line added to send command line arguments
    while(1){
        fgets(line, sizeof(line), stdin);
        printf("You sent: %s", line);
        fflush(stdout);
        if(!strncmp(line,"quit",4)) break;
    }
    printf("Signing off. Good Bye!\n");
    return(0);
}

Ruby, Run Linux Commands One by One, by Ssh and Log Everything