Unit 10
* retuen value
-- range
-- true / false
-- shell variable
* quoting
-- literal & meta
-- hard, soft, escape
-- non-meta quoting
* alias
-- set alias
-- alias & command
-- unset alias
Unit 11
* find command
-- condition & option
-- action (-exec & -ok)
* locate / slocate
-- difference to find
-- update database
* regulare expression
-- anchor
-- char set
-- modifier
* filter commands
-- cut
-- grep / egrep / fgrep
-- sort
-- head & tail
-- type / which / whereis
-- file
-- gzip / gunzip / zcat / zgrep / zmore / zless
-- join / paste
Unit 12
* shell script
-- command & script
-- script invocation (subshell & environment)
-- script running (fork & source )
-- script interpreter
-- positional parameter ($1 & $10, $@ & $#)
* HERE document
-- difference between < and <<
