#!/bin/bash
tmux new-session -d -s my_session 'ruby run.rb'

1. Create a file named my_script.sh and give it the above contents.

2. Make the file executable by running:

   chmod 755 my_script.sh
   or
   chmod +x my_script.sh

3. Then run the shell script:

   ./my_script.sh

Making the shell script executable

When you perform the chmod 755 filename command you allow everyone to read and execute the file, and the file owner is allowed to write to the file as well. You may need this for Perl and other scripts that should be run via a webserver. If you apply 755 to a directory, it means that everyone can go to it and get its file listing.

These permissions are usually translated into textual representation of rwxr-xr-x.

You can alternatively use chmod +x file_name on a file to make it executable.