The command to reattach a tmux session is tedious to type.
If you have many sessions open, or don’t remember the session name, you might type:

# List sessions
tmux ls
logs: 2 windows (created Thu Mar 13 13:07:19 2014) [237x62]
turtle: 1 windows (created Tue Mar 18 13:57:21 2014) [237x65]

# Attach to the session named turtle
tmux attach -t turtle

Create the alias

Lets create an alias to make attaching to tmux sessions easier.
The alias will allow us to autocomplete tmux session names, avoiding tmux ls.

1. Bash completion

create a new file using your preferred editor:

vim /etc/bash_completion.d/tma

Paste the following.

_tma() {
    TMUX_SESSIONS=$(tmux ls -F '#S' | xargs)

    local cur=${COMP_WORDS[COMP_CWORD]}
    COMPREPLY=( $(compgen -W "$TMUX_SESSIONS" -- $cur) )
complete -F _tma tma

Save and quit.

2. Bash alias

Add the following to your ~/.bashrc

alias tma='tmux attach -t $1'
if [ -f /etc/bash_completion.d/tma ]; then
. /etc/bash_completion.d/tma

Source your ~/.bashrc to pickup the bash_completion.

source ~/.bashrc

3. Use tma

tma turt[Tab]

If a session named turtle exists, it will complete to: tma turtle
Press enter and it will attach your tmux session.

If you have one session open, pressing tab will autocomplete it.