#!/bin/bash
# validAlphaNum -- 确保输入内容仅限于字母和数字

validAlphaNum()
{
        validchars="$(echo $1 | sed -e 's/[^[:alnum:]]//g')"
        if [ "$validchars" = "$1" ] ; then
                return 0
        else
                return 1
        fi
}

echo -n "Enter input: "
read input
if ! validAlphaNum "$input" ; then
        echo "Your input must consist of only letters and numbers." >&2
        exit 1
else
        echo "Input is valid."
fi

exit 0

image.png