#!/bin/bash

dirname=files
filename=file_0
counter=0

while [ -d "$dirname" ]
do
    dirname="${dirname%_*}"_$counter
    (( counter++ ))
done

mkdir "$dirname"
cd "$dirname"
counter=0

for a in {0..9}
do
    while [ -e "$filename" ]
    do
        filename="${filename%_*}"_$counter
        (( counter++ ))
    done

    touch "$filename"
done