Create an interactive Shell prompt menu from a dynamic list? - linux

Question

The following prompt should allow the user to make a selection based on the populated list that is outputted to an array, then prints the list with its index, and asks user to select a number from the list, then sets it to a variable. Only one choice is allowed, if user specifies an incorrect option, the script will prompt to select a correct number.
Multiple devices detected, please select one from the list:
1. Device1
2. Device2
3. Device3
1
You have selected device Device1
The code below is not functional and has many syntax errors, first I would like the script to detect if the output of arr=($(ip ad|awk '/state UP/ {print $2}')) contains multiple entries, if so run the script, otherwise set a default value.
The case statement is not dynamic however, if more then 2 cases like below it will fail, perhaps a loop?
host_interfaces()
{
arr=($(ip ad|awk '/state UP/ {print $2}'))
echo "Multiple devices detected, please select one from the list:"
for i in "${!arr[#]}"; do
printf "%s%s\n" "$i. " "${arr[$i]}"
done
PS3='Please enter your choice: '
select opt in "${arr[#]}"
do
case $opt in
"$opt")
echo "You have selected device $opt"
export HOST_INTERFACE=$opt
;;
*) echo "invalid option
break
;;
esac
done
}

Answer 1

This, maybe?
host_interfaces()
{
local opt='' h=''
arr=($(ip ad|awk '/state UP/ {print $2}'))
if [ "${#arr[#]}" -eq 1 ]; then
echo "One single device detected"
h="${arr[0]}"
elif [ "${#arr[#]}" -gt 1 ]; then
echo "Multiple devices detected, please select one from the list:"
PS3='Please enter your choice: '
select opt in "${arr[#]}"
do
case "$opt" in
"")
echo "Invalid choice"
h=''
;;
*)
echo "You have selected device $opt"
h="$opt"
break
;;
esac
done
else
echo "No device detected"
fi
echo "Selected device: ${h:-none}"
export HOST_INTERFACE="$h"
[ -z "$h" ] && return 1 || return 0
}
Note that the function returns 1 if no valid device was found or selected, else 0. So you can use it with:
if host_interfaces; then
echo "HOST_INTERFACE = $HOST_INTERFACE"
else
echo "No device selected"
fi

Answer 2

A solution:
#! /bin/bash
declare HOST_INTERFACE=
function host_interfaces() {
local -a arr=($(ip ad | awk '/state UP/ {gsub(/:/, "", $2); print $2}'))
if [ "${#arr[#]}" -eq 1 ]; then
HOST_INTERFACE="${arr[0]}"
return 0
fi
local opt=
HOST_INTERFACE=
echo "Multiple devices detected, please select one from the list:"
PS3='Please enter your choice: '
# Add "Quit" value to the items
select opt in "${arr[#]}" Quit; do
# "opt" does not contains the number but the associated value
case $opt in
"Quit")
#
break
;;
"")
# No value found
echo "invalid option"
;;
*)
echo "You have selected device $opt"
export HOST_INTERFACE=$opt
break
;;
esac
done
}
host_interfaces

Answer 3

It is possible to simply use dialog here.
dialog --backtitle "Device selection" --title "Multiple devices detected" --menu "please select one from the list:" 10 45 4 1 "Device1" 2 "Device2" 3 "Device3"
See man dialog