How do I prompt for Yes/No/Cancel input in a Linux shell script?

Question

I want to pause input in a shell script, and prompt the user for choices.
The standard Yes, No, or Cancel type question.
How d

Answer 1

You want:

• Bash builtin commands (i.e. portable)
• Check TTY
• Default answer
• Timeout
• Colored question

Snippet

do_xxxx=y                      # In batch mode => Default is Yes
[[ -t 0 ]] &&                  # If TTY => Prompt the question
read -n 1 -p $'\e[1;32m
Do xxxx? (Y/n)\e[0m ' do_xxxx  # Store the answer in $do_xxxx
if [[ $do_xxxx =~ ^(y|Y|)$ ]]  # Do if 'y' or 'Y' or empty
then
    xxxx
fi

Explanations

• [[ -t 0 ]] && read ... => Call command read if TTY
• read -n 1 => Wait for one character
• $'\e[1;32m ... \e[0m ' => Print in green
  (green is fine because readable on both white/black backgrounds)
• [[ $do_xxxx =~ ^(y|Y|)$ ]] => bash regex

Timeout => Default answer is No

do_xxxx=y
[[ -t 0 ]] && {                   # Timeout 5 seconds (read -t 5)
read -t 5 -n 1 -p $'\e[1;32m
Do xxxx? (Y/n)\e[0m ' do_xxxx ||  # read 'fails' on timeout
do_xxxx=n ; }                     # Timeout => answer No
if [[ $do_xxxx =~ ^(y|Y|)$ ]]
then
    xxxx
fi