cat -n -s
    cat -s file.txt  | tr -s ' '  | tr -s '\n' | tr 'a' 'Z'
tac / rev

split
    split -b 1G file.tar.xz "file.tar.xz.part."
    cat file.tar.xz.* | tar xJf -
    
chmod 644 755 +x -x
chown -R / chgrp -R

md5sum
  md5sum test.txt
  cat test.txt | md5sum
  echo "testing" | md5sum
  echo -n "testing" | md5sum
  
cp -rv / mv / rm -rf
sync
rsync -av --progress --dry-run -e 'ssh -p22022' --delete

find / updatedb / locate
grep / egrep / fgrep / rgrep
tar / gzip / gunzip / zcat / zless / zgrep / bzip2 ...
head -n / tail -f
hexdump -C / string / strace / ldd
dos2unix
ln -sfn
ls -ctrlh
touch
mkdir -p / cd / rmdir / tree
rm -rf
sort / uniq -c / wc -l
diff -ruN