metacharacters separation

Shell Programming and Scripting
1

I have prepared a script to submit a string in a txt file.
However there are somethings that I have to check before submitting the string in the txt file.
One of those checks is to determine whether the string entered contains any metacharacters.
I have tried sth like;

echo "string" | grep -v [a-zA-Z0-9]
echo "string" | egrep -v .|,|!

however it doesn't work.
How can i check whether the string entered includes any metacharacters or not?

2 
case "$string" in
     *[!a-zA-Z0-9]*) echo "non alphnumeric" ;;
     *) echo OK ;;
esac
3

thank you for the response however
this one didn't work since i 'm using a sentence as a string.
here is the response;

>more alphanumeric.sh
case "$1" in
     *[!a-zA-Z0-9]*) echo "non alphnumeric" ;;
     *) echo OK ;;
esac
>./alphanumeric.sh "this sentence doesn't contain any metacharacters"
non alphnumeric
>./alphanumeric.sh "this sentence contains * metacharacters"
non alphnumeric

###
also other than the alphanumerics, my sentence can also contain . or , or !
Can you help me with this?

4

Add whatever characters you want to allow to the pattern, e.g.:

case "$string" in
     *[!a-zA-Z0-9\ !]*) echo "not OK" ;;
     *) echo OK ;;
esac