This command is very useful when renaming a large group of photographs that were taken by a digital camera.  A digital camera usually names the photographs with a numbering system such as DSC001 or by using some other number that acts as a date and time stamp.  This takes the file names and numbers them in order to three place values starting at 001.jpg.  In the beginning of the script, I am searching for .JPG with the letters capitalized.  I like to change the capital .JPG extension to lowercase so that it matches the image extension of my phone to keep my files consistent.  Make adjustments to the capitalization or extension as needed.

find . -name '*.JPG' | awk 'BEGIN{ a=1 }{ printf "mv \"%s\" %03d.jpg\n", $0, a++ }' | bash