Execute a list of Unix commands using ssh

Question

I want to run the same set of Unix commands on multiple machines. I am aware of ssh and something like the below. I want to write a shell script to do this. I have access to bash and ksh and I'm on Linux Red Hat 5.

ssh root@ip "echo \$HOME"

However, I have 2 questions:

1. I keep getting prompted for a password. How can I have it not prompt me and enter the password automatically?
2. How can I execute multiple commands?

Answer 1

1. You should use key based authentification, possibly coupled with ssh-agent to remember key passphrase.

2. You can invoke sh -c as the command, and pass it a string containing the list of command to execute. ssh invoke a shell on the remote machine, so you can pass a list of command as a string.

For example:

$ ssh user@ip "echo 'Hello world'; whoami; cd / ; ls"

Answer 2

Use ssh-agent to set up authentication for all commands. Or put your multiple commands into a single shell script.

Answer 3

2. Send a list of commands to the remote shell. Possible solutions:

   • use ", escape line breaks to format code and end each substatement with ;.
     Disadvantage: " should not be used inside the command list.

     ssh user@ip "\
       echo 'Hallo sir, how are you doing?';\
       whoami;\
       cd /;\
       ls\
     "
     

   • use ' and format code with regular line breaks.
     Disadvantage: ' should not be used inside the command list.

     ssh user@ip '
       echo "Hallo sir, how are you doing?"
       whoami
       cd /
       ls
     '
     

Note: using " or ' inside the respective statements will not necessarily result in an error. Though you may get unsuspected results.