Functions

A Bash function groups commands under a name you can call repeatedly — but unlike most languages, it can only hand a numeric exit status back to whoever called it, not an arbitrary value.

Defining and calling a function

#!/bin/bash
greet() {
    echo "Hello, $1!"
}

greet "Sam"
greet "Priya"

Hello, Sam!
Hello, Priya!

Inside a function, $1, $2, and so on refer to that function's own arguments — not the script's overall command-line arguments, even if the function happens to be called with none.

Local variables

Without local, a variable set inside a function is global by default and can quietly overwrite a variable of the same name elsewhere in the script:

#!/bin/bash
message="outer"

show_message() {
    local message="inner"
    echo "Inside function: $message"
}

show_message
echo "Outside function: $message"

Inside function: inner
Outside function: outer

"Returning" a value

return only sets a numeric exit status (0–255), checked afterward with $? — it can't send back text. To hand back an actual value like a string or number, echo it and capture that output with $(...):

#!/bin/bash
double() {
    echo $(( $1 * 2 ))
}

result=$(double 21)
echo "Result: $result"

Result: 42