Use the -n/-i flags to avoid overwriting files with cp and mv
The mv and cp builtins have a -n flag (no-clobber), and will prevent them from overwriting an existing file. They also have a -i flag (interactive)
I saw these flags mentioned in a Discord; I wanted to do a few experiments to see how they work in practice (and whether they’d be useful for me). I ran these tests with the macOS tools, but they may differ on other platforms.
cp
This will prevent overwriting files, and gives you a distinct exit code if it’s unable to copy the file.
Here’s an example:
echo "red triangle" > shape.txt
echo "blue circle" > new_shape.txt
cp -n new_shape.txt shape.txt
echo "$?" # --> 1
cat shape.txt # --> red triangle
cp new_shape.txt shape.txt
echo "$?" # --> 0
cat shape.txt # --> blue circle
If you use cp -i, it has similar behaviour, returning different exit codes depending on whether or not the filw as overwritten:
echo "red triangle" > shape.txt
echo "blue circle" > new_shape.txt
cp -i new_shape.txt shape.txt # --> n
echo "$?" # --> 1
cat shape.txt # --> red triangle
cp -i new_shape.txt shape.txt # --> y
echo "$?" # --> 0
cat shape.txt # --> blue circle
mv
This will prevent overwriting files, but it always has exit code 0, whether or not it moved the file.
Here’s an example:
echo "red triangle" > shape.txt
echo "blue circle" > new_shape.txt
mv -n new_shape.txt shape.txt
echo "$?" # --> 0
ls # --> new_shape.txt shape.txt
mv new_shape.txt shape.txt
echo "$?" # --> 0
ls # --> shape.txt
And the same exit codes if you overwrite a file (or not) with mv -i:
echo "red triangle" > shape.txt
echo "blue circle" > new_shape.txt
mv -i new_shape.txt shape.txt # --> n
echo "$?" # --> 0
ls # --> new_shape.txt shape.txt
mv -i new_shape.txt shape.txt # --> y
echo "$?" # --> 0
ls # --> shape.txt