Local and Global Shell variable (export command)

Normally all our variables are local. 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. For e.g. Consider following example
$ vech=Bus
$ echo $vech
Bus
$ /bin/bash
$ echo $vech

NOTE:-Empty line printed
$ vech=Car
$ echo $vech
Car
$ exit
$ echo $vech
Bus

Command	Meaning
$ vech=Bus	Create new local variable 'vech' with Bus as value in first shell
$ echo $vech	Print the contains of variable vech
$ /bin/bash	Now load second shell in memory (Which ignores all old shell's variable)
$ echo $vech	Print the contains of variable vech
$ vech=Car	Create new local variable 'vech' with Car as value in second shell
$ echo $vech	Print the contains of variable vech
$ exit	Exit from second shell return to first shell
$ echo $vech	Print the contains of variable vech (Now you can see first shells variable and its value)

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

Command	Meaning
$ vech=Bus	Create new local variable 'vech' with Bus as value in first shell
$ echo $vech	Print the contains of variable vech
$ export vech	Export first shells variable to second shell i.e. global varible
$ /bin/bash	Now load second shell in memory (Old shell's variable is accessed from second shell, if they are exported )
$ echo $vech	Print the contains of variable vech
$ exit	Exit from second shell return to first shell
$ echo $vech	Print the contains of variable vech