Touch , Tee , Tr

Tee ---> Put output on screen and appened to file

Test
Check for a file ---> test -a
Check for beeing root --> test -O /usr/bin/su
Check for astrin beeinfg non null ---> test -n "$foo"

Compare two strings numerically ---> test $var1 -gt $var2

In a ksh script one uses "test" indirectly --> if [-a ]]; then -- :fi ;