The solution to the above example, using rename:
rename -v -n 's/file_\d{1,3}/upl/' file_*.png
Usage:
rename [options] [Perl regex search/replace expression] [files]
From man rename:
-v, --verbose
Verbose: print names of files successfully renamed.
-n, --no-act
No Action: show what files would have been renamed.
rename MAY take regex as the arguments.
What we are looking at is the content between the single quotes '. You can place regex separated by /.
Formula: s/(1)/(2)/ where (1) = search pattern, and (2) = replace pattern.
So, familiarize youself with regex, and enjoy pattern based batch file renaming!