Bash

One line conditional

Both the following lines will write to the screen "false"

 [[ 1 == 0 ]] || echo "text"

 [[ 1 == 1 ]] && echo "text"

Check for environment variable

This will check to see if an variable is set

 if [[ -z "$var" ]]; then
   echo "var is not set"
 fi

Change the command prompt.

To change the command prompt, export the below value.

 export PS1=">"

or

 export PS1="${ret_status} %{$fg[cyan]%}%c%{$reset_color%} $(git_prompt_info)"