Local variable can be used in same shell, if you load another copy of shell (by typing the /bin/bash at the $ prompt) then new shell ignored all old shell's variable.
Global shell defined as: "You can copy old shell's variable to new shell (i.e. first shells variable to seconds shell), such variable is know as Global Shell variable."
To set global varible you have to use export command.
Syntax:
export variable1, variable2,.....variableN
Examples:
$ vech=Bus
$ echo $vech
Bus
$ export vech
$ /bin/bash
$ echo $vech
Bus
$ exit
$ echo $vech
Bus
