Find file name 
find / -type f -name RRDs.pm

Find folder name
find / -type d -name ‘folder name’

Find text
find /into/this/dir -name ‘*.php’ -print0 | xargs -r -0 grep -l texttofind

Sort file size in reverse order
ls -lSr

Show last rows of file
tail -f filename

Display active process
ps -w | grep spamd

info processor architecture
cat /proc/cpuinfo | grep model

Zip compress
zip -rv file.zip folder_to_zip
unzip -v filename.zip

To extract all members of letters.zip into the current directory only:
unzip -j letters

To test letters.zip, printing only a summary message indicating whether the archive is OK or not:
unzip -tq letters

To test all zipfiles in the current directory, printing only the summaries:
unzip -tq \*.zip