Create your shell script as login.sh in your $HOME folder.
Paste the following one-line script into Script Editor:
do shell script "$HOME/login.sh"
Then save it as an application.
Finally add the application to your login items.
If you want to make the script output visual, you can swap step 2 for this:
tell application "Terminal"
activate
do script "$HOME/login.sh"
end tell
If multiple commands are needed something like this can be used:
tell application "Terminal"
activate
do script "cd $HOME"
do script "./login.sh" in window 1
end tell