Command line
text files
magic string
permissions
script files
conditionals if, else
loops while
test [ [[ -e -ne
gnu.org
portability and readability
math (eval)
strings printf, echo
user input
parsing parameters
offering help
filesystem conventions and standards
redirection
shell utilities grep, cat
other tools screen, nohup
backgrounding
top
tr
sending mail
set, IFS, OFS
regular expressions
debugging set -x
safe coding -quotes, deleting with find