Find large files over 100mb on the filesystem:
find / -type f -size +100000k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'
Remove empty directories (recursive)
find -depth -type d -empty -exec rmdir {} \;
Replace character (char1) in Linux filenames with another (char2)
for filename in `ls` ; do mv $filename `echo $filename | sed s/char1/char2/` ; done
Replace spaces in filenames with underscores
for file in *; do mv "$file" `echo $file | sed -e 's/ */_/g' -e 's/_-_/-/g'`; done