Example of how to call a function in a Linux Shell Script - passing in input parameters and receiving the result from the function (in a way that resembles modern programming languages)

welcome.sh

# a global variable 
WELCOME_ROOT=Hello

# invoke this function with two arguments:
# 1. (FROM_VAR) the name of the greeter 
# 2. (TO_VAR) the name of the greetee
# this function returns a welcoming message
get_welcoming_message()
{
  FROM_VAR=$1
  TO_VAR=$2

  # local variable THE_MESSAGE is used while composing the result; it is not accessible from outside the function
  local THE_MESSAGE=""
  THE_MESSAGE="$WELCOME_ROOT to $TO_VAR from $FROM_VAR" 
  THE_MESSAGE="$THE_MESSAGE !!!"
  # this line provides the output from this function; this output can be captured in a variable by the caller using VAR=$(function param1)  
  echo "$THE_MESSAGE"
}

GUEST=Joe
# invoke function get_welcoming_message with two arguments (Jack and $GUEST) and capture the result in variable WELCOME_MESSAGE 
WELCOME_MESSAGE=$(get_welcoming_message "Jack" $GUEST)
echo "message= $WELCOME_MESSAGE"