1. translate (tr)

tr     - translate
         -d - delete
            \! - exclamation should be back-slashed even in brackets
            \n - newline

tr 'A-Z' 'a-z' - translage upper to lower case


2. sorting (sort)

sort -u ...
  sort and uniq togeather

3. duplicates removal (uniq)

4. relational database operator (join)

join     -
           -v1 - only in input source 1

join -v1 my_file vocab_words - get errors (words not from a dictionary)


5. search the "whatis" database for strings (apropos)

apropos database | grep (1)   - commands that have "database" in description

6. Test file/directory properties

test, [

7. Environment variables

printenv

8. Terminal settings

stty -a
	print all current settings
stty intr '^t'
	Use C-t (instead of C-c) to interrupt the job
stty intr '^-'
	Unset interrupt-function at all

9. Named pipes

mkfifo <pipe-name>