Find

Convert all your files saved as "*.jpg-large" back to "*.jpg" (so Twitter thinks they are images again)
find. -depth -name "*.jpg-large" -exec sh -c 'f="{}"; mv -- "$f" "${f%.jpg-large}.jpg"' \;

Delete all zero-length files in a directory
find. -size 0 -exec rm {} \;

Find files by name
find. -name *wav -print

Get a word count for each file with extension .001
find. -name "*.001" -exec wc -w {} \;

Remove empty directories under the working directory
find. -empty -exec rm -rf {} \;

Replace spaces in the filename of all the files in a directory with hyphens
find. -name "* *mp3" -exec rename 's/\ /-/g' {} \;

Scan your Calibre library recursively and copy the text files to a single directory
find. -name "*.txt" -exec cp {} /home/teresita/Desktop/text \;