Menu: Difference between revisions

This example uses [[Bash]] with its [http://www.softpanorama.org/Scripting/Shellorama/Control_structures/select_statements.shtml select] statement, but Bash did not invent this feature. The ''select'' loop comes originally from the [[Korn Shell]], and appears in some other shells.

{{works with|ksh93}}

{{works with|zsh}}

<lang bash># choose 'choice 1' 'choice 2' ...

# Prints menu to standard error. Prompts with PS3.

# Reads REPLY from standard input. Sets CHOICE.

choose() {

CHOICE= # Default CHOICE is empty string.

[[ $# -gt 0 ]] || return # Return if "$@" is empty.

select CHOICE; do # Select from "$@".

if [[ -n $CHOICE ]]; then

break

else

echo Invalid choice.

fi

done

}

PS3='Which is from the three pigs: '

choose 'fee fie' 'huff and puff' 'mirror mirror' 'tick tock'

[[ -n $CHOICE ]] && echo You chose: $CHOICE

[[ -z $CHOICE ]] && echo No input.</lang>

<pre>$ bash menu.sh

Invalid choice.

Which is from the three pigs: 2

You chose: huff and puff

$</pre>

Our ''choose'' function wraps a ''select'' loop. This wrapper implements the task requirement to provide an empty string from an empty list of choices. It also breaks the ''select'' loop after the first good choice. A ''select'' loop always continues until the script breaks the loop, or the standard input reaches end of file (EOF).

If the user enters a blank line, the ''select'' loop repeats the list of choices. This is the only way to print the list again. An invalid choice only repeats the prompt, not the list.

[[Z Shell]] prints choices in multiple columns. This is good for menus that have many choices.

<pre>$ zsh scratch.sh

1) fee fie 2) huff and puff 3) mirror mirror 4) tick tock

You chose: huff and puff</pre>