Create new file but add number if filename already exists in bash

The following script can help you. You should not be running several copies of the script at the same time to avoid race condition.

name=somefile
if [[ -e $name.ext || -L $name.ext ]] ; then
    i=0
    while [[ -e $name-$i.ext || -L $name-$i.ext ]] ; do
        let i++
    done
    name=$name-$i
fi
touch -- "$name".ext