1.How to set\unset an environment variable in unix
ENVIRONMENT variables are set using the setenv command, displayed using the printenv or env commands, and unset using the unsetenv command.
To show all values of these variables, type
% printenv | less
2.what is the difference between PATH and path in UNIX
In general, environment and shell variables that have the same name (apart from the case) are distinct and independent in Unix.
PATH represents an environment variable where as path represents a shell variable.