Why is my bash randomly selecting files and renaming? - macos

Question

On my Mac I am terminal scripting an increment rename of some files in a folder. The files have a number at the end but from a top down approach they are in order:
foobar101.png
foobar107.png
foobar115.png
foobar121.png
foobar127.png
foobar133.png
foobar141.png
foobar145.png
foobar151.png
foobar155.png
When I create and run my loop it works:
DIR="/customlocation/on/mac"
add=1;
for thefile in $(find $DIR -name "*.png" ); do
cd $DIR
mv -v "${thefile}" foobar"${add}".png
((add++))
done
However, when it runs the increment it's not as expected:
foobar101.png -> need foobar1.png but is foobar10.png
foobar107.png -> need foobar2.png but is foobar3.png
foobar115.png -> need foobar3.png but is foobar4.png
foobar121.png -> need foobar4.png but is foobar2.png
foobar127.png -> need foobar5.png but is foobar9.png
foobar133.png -> need foobar6.png but is foobar6.png
foobar141.png -> need foobar7.png but is foobar1.png
foobar145.png -> need foobar8.png but is foobar5.png
foobar151.png -> need foobar9.png but is foobar8.png
foobar155.png -> need foobar10.png but is foobar7.png
Ive tried searching on SO, Linux/Unix, Ask Ubuntu, and SuperUser but I don't see any questions that solve the issue of controlling the increment and I dont know if it's something in particular I should be looking at. So how can I control the increment from the lowest number/filename instead of the Mac possibly randomly renaming with an increment so I get the desired output?
EDIT:
After a comment from Etan I was looking into the numerical values at the end and some of the files are named foobarXXXX and that is the issue. The below answer, while awesome and a new approach I will look into still produces the same outcome because of some other files. If I remove all files that are foobarXXXX and only leave files with values of foobarXXX my code and the code in fedorqui's answer work. Is there a way then I can target this while in the loop process or do I have to target all names and test to see the length of values and adjust accordingly?

Answer 1

You cannot rely on the order of a find command, which uses the order that the VFS gives them to it in.
You may, instead, want to sort it:
DIR="/customlocation/on/mac"
add=1;
while IFS= read -r thefile; do
cd $DIR
mv -v "${thefile}" foobar"${add}".png
((add++))
done < <(find $DIR -name "*.png" | sort)
#-------^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Note this uses process substitution, which feed the while loop:
Process substitution is a form of redirection where the input or
output of a process (some sequence of commands) appear as a temporary
file.