This function checks if an defined function or command exist.

function_exists.bash

# This function checks if an defined function or command exist.
#
#  @param string $1 function name (required)
#  @return bool
#  @example:    is_function "rc_myfunc" || exit 1
 
is_function() {
  type "$1" &>/dev/null && return 0 || return 1
}