Validating user input in Linux

Question

I need to make program in Linux that will find Pictures in folder. Like JPEG, PNG, BMP. And I need to make it robbust to invalid input. Like when I write LoL instead of png it will write error.Here is my code yet:

#!/bin/bash

echo "Input what you are searching for :"
read subor

echo "-----------------------"

if [ $subor != "png" ];
then 
    echo
    echo "Nebol zadaný vstup pre PNG"
    echo
else
    Path=$ cd /home/zps/Pictures/
    command=$ find -type f -exec file --mime-type {} \; | awk '{if ($NF == "image/png") print $0}' | wc -l
fi

if [ $subor != "jpeg" ];
then 
    echo
    echo "Nebol zadaný vstup pre JPEG"
    echo
else
    Path=$ cd /home/zps/Pictures/
    command=$ find -type f -exec file --mime-type {} \; | awk '{if ($NF == "image/jpeg") print $0}' | wc -l
fi

if [ $subor != "bmp" ];
then 
    echo
    echo "Nebol zadaný vstup pre BMP" 
    echo
else
    Path=$ cd /home/zps/Pictures/
    command=$ find -type f -exec file --mime-type {} \; | awk '{if ($NF == "image/bmp") print $0}' | wc -l
fi

echo "-----------------------"

I tried something from internet but I just couldnt do it. I tried to make some code, and it works, I just cant figure it out how to make error when user input someting else that I want. I just need JPEG, PNG and BMP.

Btw: Please paste your script at shellcheck.net and try to implement the recommendations made there. — Cyrus
– Cyrus, Commented Mar 31, 2022 at 21:06

Barmar · Accepted Answer · 2022-03-31 20:03:27Z

2

Use a case statement to match all the allowed types. Then you can use a *) case to catch the invalid input.

case "$subor" in
    png) ... ;;
    jpeg) ... ;;
    bmp) ... ;;
    *) echo "Please enter png, jpeg, or bmp" ;;
esac

answered Mar 31, 2022 at 20:03

Barmar

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