CTRL+r to do reverse command search, keep hitting CTRL+r to move up through all previous uses of the command. Eg:
$ ~ ls /media/xy
bck-i-search: ls_
man -f ls #-f='what is' gives a one line answer
direct both STOUT and STERR with &> logfile
find only non blank lines (-v '^$')
Use sed to pattern match from a file and write that to a new file:
# sed -n '/pattern/w target_file' source_file.txt
chmod u=rwx,g=rx,o= file
chmod u+rwx file
chmod g-x file
chmod ugo-x file
chmod a+r file
| sort -rn -k 4 #reverse numerical order and using the fourth field as the key.
$ ls -l | awk '/\.txt$/{total += $5; print} END{print total}'