Answer by CAB for multiple file rename based on modification date

Having done something like this before, I can assure you it's easy to make a typo that will give you an even larger problem that you already have. Use this information at your own risk.

At bash prompt;

i=0 ; for f in `ls -rt` ; do i=$(expr $i + 1); mv $f $i.txt; done

• i acts as a counter
• ls -rt lists files in reverse order by modification time - if you've copied, moved or otherwise modified the files, this may not give you the file ordering you expect. Check it carefully by running ls -rt as a separate command and check it - twice.
• for f inls -rt; do iterates of the list of files with 'f' taking on each file name
• i=$(expr $i + 1) increments the counter
• mv $f $i.txt renames the file using the counter, and adding the .txt extension
• done closes the loop
• note that commands in the loop are separated by semicolons, so if you add another command, follow it with a semicolon