Recognize file headers and rename file extensions

testfile.sh

#!/bin/bash

# test all files
for file in *; do
    if [ -f "$file" ]; then
        # read first 3 bytes
        bytes=$(head -c 3 "$file" | od -An -t x1 | tr -d ' \n')

        # test file bytes
        case $bytes in
            504b03)
                # ZIP
                mv "$file" "${file}.zip"
                ;;
            ffd8ff)
                # JPG
                mv "$file" "${file}.jpg"
                ;;
            255044)
                # PDF
                mv "$file" "${file}.pdf"
                ;;			
            524946)
                # WEBM
                mv "$file" "${file}.webm"
                ;;			
            # Others
            *)
                # not match
                ;;
        esac
    fi
done