Bash Parameters and Variables

Internal

• bash Concepts
• bash Environment Variables

Global Variable

Global variables are only maintained within the context of the current shell. Once the shell exits, the global variables are discarded.

The value of a global variable is not available to sub-shells, unless the variable is exported.

export

export VAR=VALUE

Declaring a global variable to be exported causes the variable and its value to be copied in the environment of a invoked sub-shell. The sub-shell gets a copy of the variable, not a reference. Modifying the variable from the sub-shell does not reflect into the value of the global variable maintained by the invoking shell.

Variables exported by Sub-Shells

If a sub-shell invoked from another shell exports a global variable, once the sub-shell exits, the exported variables are discarded, and the invoking shell does not sees them.

Local Variable

The local keyword designates a local variable. Local variables can only be declared inside a function.

Scope

All variables declared in a shell are visible inside the functions executed within that shell and inside functions invoked from function invoked from the shell, recursively.