Bash Completion for My EC2 Management Script

May 9, 2023

I like efficiency and minimizing keystrokes.

For my EC2 management script, I needed to specify the host’s name like this:

ec2 start some_host_name

I didn’t really want to type out the host name every time, so I threw together an autocompletion script.

This way, I can type this:

ec2 start so<tab>

and have it autocomplete to this:

ec2 start some_host_name

I don’t do completions all the time, so a good guide is An Introduction to Bash Completion.

I started with my completion script that looks like this:

ec2_bash_completion:

# Adds tab-completion of SSH config Hosts to the ec2 command.
#
# Install by putting this line in your .bash_profile or .bashrc.
#
#     . $HOME/path/to/ec2_bash_completion
#
# Then reload with `. ~/.bashrc`.

_ec2_hosts()
{
    # Get a list of hostnames from ~/.ssh/config
    local hosts=$(grep -E "^Host\s+" ~/.ssh/config | awk '{print $2}')

    # Get the current word being completed
    local current_word="${COMP_WORDS[COMP_CWORD]}"

    # Set the list of possible completions to the list of hosts
    COMPREPLY=($(compgen -W "${hosts}" -- "${current_word}"))
}

# Register the custom completion function for the "ec2" command
complete -F _ec2_hosts ec2

The script needs to be saved, made executable, and sourced in your .bashrc with one of these two lines:

. /path/to/ec2_bash_completion

# Or

source /path/to/ec2_bash_completion

Exit and save your .bashrc, then source it with . ~/.bashrc. Now your completions will work!

This script doesn’t complete “start|stop”, but if I add more commands, maybe I’ll update the script.