73.Function_Variable_Scopes.md

Variable Scope in Shell Scripting

Global Variables

By default, every variable in a shell script is global, meaning it can be accessed anywhere within the script. However, a variable must be declared before it is used.

Example 1:

#! /bin/bash
f1() {
    echo "x value: $x"
}
x=10
f1

Output:

x value: 10

Example 2:

#! /bin/bash
f1() {
    x=20
    echo "x value: $x"
}
x=10
f1
echo "After f1 execution x value: $x"

Output:

x value: 20
After f1 execution x value: 20

Example 3:

#! /bin/bash
f1() {
    echo "x value: $x"
}
f1
x=10
f1

Output:

x value:
x value: 10

Example 4:

#! /bin/bash
f1() {
    x=10
}
f1
echo "x value: $x"

Output:

x value: 10

Local Variables

To restrict a variable's scope to a function, use the local keyword. These variables can only be accessed within the function and are not available outside of it.

Example:

#! /bin/bash
f1() {
    local x=10
    echo "Inside function x value: $x"
}
f1
echo "Outside function x value: $x"

Output:

Inside function x value: 10
Outside function x value:

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Return Statement in Functions

Every function in shell scripting returns a value, with the default being the exit code of the last command in the function. You can explicitly return values using the return statement.

• Syntax: return <exitcode>
• Allowed values for <exitcode>: 0 (success) to 255 (failure).

Example:

#! /bin/bash
sum() {
    if [ $# != 2 ]; then
        echo "You should pass exactly two numbers"
        return 1
    else
        echo "The SUM: $(($1 + $2))"
    fi
}
sum 10 20
echo "The Return value of this function: $?"
echo
sum 10
echo "The Return value of this function: $?"

Output:

The SUM: 30
The Return value of this function: 0

You should pass exactly two numbers
The Return value of this function: 1

---

Use Case Example

backup() {
    # Commands to take backup
}
backup
if [ $? != 0 ]; then
    echo "Backup failed"
else
    echo "Backup successful"
fi

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Break vs Exit vs Return

1. break: Used inside loops to terminate loop execution and continue with statements after the loop.
2. exit: Terminates script execution immediately, preventing further statement execution.
3. return: Used inside functions to terminate function execution. After the return statement, subsequent statements in the function are skipped, but the script continues executing after the function call.

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