[SOLVED] [Bash]declare -i error message

gerard4143 · 05-15-2024, 02:34 AM

Code:

#! /usr/bin/env bash
set -euo pipefail

declare -i num1=0

read -r -p 'Enter first number: ' num1

echo "You entered: ${num1}"

How can I display a message(better than the default) when the user enters a non-integer value for num1?

shruggy · 05-15-2024, 03:18 AM

Well, Zsh has got try-blocks, but Bash doesn't have anything like this AFAIK.

pan64 · 05-15-2024, 03:42 AM

Code:

read -r -p 'Enter first number: ' num1 || { here comes the error handling }

In general this is how you can handle errors in shell. But not in this case, because entering a non-integer string will not cause an error (but set num1 to 0).
You can do:
1. allow to read anything and check if it is a number
2. do not accept if num1=0
3. do nothing

shruggy · 05-15-2024, 04:54 AM

@pan64. Have you tried it? It doesn't work in this case. I was thinking perhaps

Code:

trap 'echo Wrong; exit 1' ERR

would help, but that didn't work either. Trapping on EXIT does work though, so you can at least add your own message to that of Bash.

pan64 · 05-15-2024, 05:44 AM

Quote:

Originally Posted by shruggy

@pan64. Have you tried it? It doesn't work in this case. I was thinking perhaps

Code:

trap 'echo Wrong; exit 1' ERR

would help, but that didn't work either. Trapping on EXIT does work though, so you can at least add your own message to that of Bash.

what do you mean? I mean what should be tried?

shruggy · 05-15-2024, 05:55 AM

The code from the first post.

pan64 · 05-15-2024, 05:57 AM

yes, I tried. And I also wrote it won't work in this case.

shruggy · 05-15-2024, 06:00 AM

Ah sorry, my fault. I didn't read your post thoroughly.

MadeInGermany · 05-16-2024, 12:48 PM

Allow all input then check for an integer:

Code:

#!/bin/bash

declare -i num1=0
 
while
  read -r -p 'Enter first number: ' inp
  [[ ! $inp =~ ^[-+]?[0-9]+$ ]]
do
  echo "bad input, try again" >&2
done
num1=$inp
 
echo "You entered: ${num1}"

Within [[ ]] the =~ operator checks the LHS against an extended regular expression (ERE).
Can also be done with the == or != operator that checks the LHS against an extended glob:

Code:

  [[ $inp != ?([-+])+([0-9]) ]]

pan64 · 05-16-2024, 01:46 PM

the most interesting way to do it is:

Code:

declare -i num1=0
read -r -p 'Enter first number: ' inp
read -r num1 <<<"$inp"
[[ $num1 = $inp ]] || whoopppps

(Or just an idea)