How to check for bad filename or path in BASH

So, I am reading about injection attacks.  White Listing is better than Black Listing.

Bash support some regex.

The first IF – check for a valid file name.

2nd checks for a Unix path name and allows spaces.  But not “&, >, <, or | “.  Ampersand in Linux is really bad.  if you allow that in certain user inputs and pass it to Bash – it could potentially execute a devastating script injected in.  ( rm -rf / comes to mind )

if ! [[ $4 =~ ^[0-9a-zA-Z._-]+$ ]]; then
    # Checks whether valid characters exist
    echo "bad file name";
    exit
fi

if ! [[ $2 =~ ^[0-9a-zA-Z._-\/\ ]+$ ]]; then
    # Checks whether valid characters exist
    echo "suspicious path";
    exit
fi