keep renaming until file doesnt exist in directory - bash

Question

I need to check if a file exists in a directory, if it does rename it by adding an extra extension like original.txt to original.txt.txt. BUT check whether the renamed file still exist.
My code only changes it one time and is not checking the rest of the contents before it renames it. It just overwrites all my original.txt.txt
Question:
How to check all files and add .txt as many times as needed so it doesn't conflict with any other name in directory.
if [ -e "$destination_folder/$basename_file" ]
then
cp "$file_name" "$destination_folder/$basename_file".txt
fi

Answer 1

If I understand you correctly, you want to rename a file only if there is no other file of the new name. This you want to prevent accidental overwriting of this other file.
To achieve this you can use mv (which I assume you use for renaming) with the option -i so it will ask before overwriting anything. In case you are quite sure you do not want to rename anything then, you can pipe yes n into the mv command:
yes n | mv -i "$old" "$new"
To prevent seeing ugly automatically answered questions, you can redirect the stderr of the commands to /dev/null:
(yes n | mv -i "$old" "$new") 2> /dev/null
This will now rename the file only if the new name is free. Otherwise it does nothing.
EDIT:
You can use a loop to find a "free" name:
name=$original
while [ -e "$name" ]
do
name="$name.txt"
done
mv "$original" "$name"
This way you will find a free name and then use it.
Be aware that this can still overwrite a just recently created file of the new name. Unix systems are multitasking and another process could create a file of the new name just after the loop and before the mv command.
To avoid this pathological case (in case you cannot be sure that this won't happen), you should use my method above to move only if nothing would be overwritten, and afterwards you should check if the original file (with the original file name) still exists, and if it still exists, try the whole thing again:
new=$old.txt
while true
do
(yes n | mv -i "$old" "$new") 2> /dev/null
if [ -e "$old" ]
then
new=$new.txt
else
break
fi
done