Mac Terminal batch file rename: flip string and digits - regex

Question

I read some threads about batch renames in Mac OS X Terminal and understood you can do something like this:
for file in *.pdf
do
mv "$file" "<some magic regex>"
done
As you can guess, my issue is with the regex for this particular purpose:
Old file
Author-Year-Title.pdf
New file
Year-Author-Title.pdf
I did try some regex code but got stuck. I "just" want to flip Author and Year, but cannot figure out how. Any help would be appreciated.

Answer 1

This will do, or come quite close to doing, what you are asking for. The technique I am using is called Bash Parameter Substitution and it is documented and described very well here.
#!/bin/bash
for file in *.pdf
do
echo DEBUG: Processing file $file
f=${file%.*} # strip extension from right end
author=${f%%-*} # shortest str at start that ends with dash
title=${f##*-} # shortest str at end that starts with dash
authoryear=${f%-*} # longest string at start that ends in dash
year=${authoryear#*-}
echo DEBUG: author:$author, year:$year, title:$title
echo mv "$file" "$year-$author-$title.pdf"
done
Basically, I am extracting the Author, Year and Title into variables for you and then you can put them together in whatever order you like with whatever separators you like at the end and do the actual renaming. Note that the script actually does nothing until you remove the echo statement in front of the mv command so you can test it out and see what it would do.
Please practice on a COPY of your data in a spare, temporary directory.
Sample Output
DEBUG: Processing file Banks-2012-Something.pdf
DEBUG: author:Banks, year:2012, title:Something
mv Banks-2012-Something.pdf 2012-Banks-Something.pdf
DEBUG: Processing file Shakey-2013-SomethingElse.pdf
DEBUG: author:Shakey, year:2013, title:SomethingElse
mv Shakey-2013-SomethingElse.pdf 2013-Shakey-SomethingElse.pdf
If you like ugly sed commands you can do it more succinctly like this:
#!/bin/bash
for file in *.pdf
do
echo DEBUG: Processing file $file
new=$(sed -E 's/(.*)-([0-9]{4})-(.*)\.*/\2-\1-\3.pdf/' <<< $file)
echo $new
done
The s/xxx/yyy/ means substitute or replace xxx with yyy. Anything inside parentheses must be captured as capture groups and then the first capture group becomes available as \1 in the replacement and the second capture group becomes available as \2 and so on. So it says... save anything up to the first dash as \1, exactly 4 digits between the next pair of dashes as \2 and the other stuff as \3, and then it prints the captured groups out in a different order.