Functions

• functions can be terminated using return OR exit

  • in Bash, return does not pass a data value like in C++ or Java; it only passes an exit status code (a number between 0 and 255).

    check_network() {
        ping -c 1 google.com > /dev/null 2>&1
        if [ $? -eq 0 ]; then
            return 0 # Success
        else
            return 1 # Failure
        fi
    }

    Risk	Explanation
    The 255 Limit	Exit codes are 8-bit integers. If your math result is 256, return will give you 0. If it is 257, it gives you 1. It “wraps around”.
    Status vs. Data	In Linux, 0 usually means “Success” and non-zero means “Error”. Using return for math flips this logic and can confuse other parts of your script.
    Immediate Capture	You must use $? immediately. If you run any other command (even an echo) between the function call and $?, the value will be overwritten by the new command’s status.

• local used to define local variables inside function which are different from outside variables..

  • TIP: if we try to access a variable in bash which is not defined.. we won’t get any errors!!! instead it prints empty value..

• We can’t directly access inner function of a function! first we have to call outer-function which then defines inner function for global access..

Possible Function Sytaxes and stuff…

• name() { ... }: Standard syntax; the most portable and common way to define a function.

• function name { ... }: Alternative syntax using the function keyword; parentheses are optional here.

• function name() { ... }: Combined syntax; works in Bash but is redundant.

• name() { command; }: Single-line syntax; requires a space after { and a semicolon before }.

• local var=$1: Variable scope limiter; restricts a variable’s existence to the function execution.

• $1, $2, ... $n: Positional parameters; accesses arguments passed to the function by their order.

• $#: Argument counter; returns the total number of arguments passed to the function.

• $@: All-arguments list; represents every passed argument as a distinct quoted string.

• return n: Exit status; stops the function and returns a numeric code (0–255) to the caller.

• $(name): Command substitution; captures the echo output of a function into a variable.

• name() { ... } > file: Function redirection; sends all standard output from the function into a specific file.

• outer() { inner() { ... }; }: Nested definition; defines a function inside another (inner becomes global once outer runs).

  parent_func() {
      echo "This is the parent."
  
      child_func() {
          echo "This is the child, nested inside."
      }
  
      child_func  # Calling it inside the parent
  }
  
  # child_func  # This would fail here (not defined yet)
  parent_func   # Runs parent and defines child
  child_func    # Now this works globally!

Example