check_if_dir.sh

#!/bin/bash
#  funcback.sh : Use $FUNCNAME
backup(){
	local d="$1"
	[[ -z $d ]] && { echo "${FUNCNAME}(): directory name not specified"; exit 1; }
	echo "Starting backup..."
}

backup $1



#!/bin/bash
file="$1"

# User-defined function
is_file_dir(){
        # $f is local variable
	local f="$1"
        # file attributes comparisons using test i.e. [ ... ]
	[ -f "$f" ] && { echo "$f is a regular file."; exit 0; }
	[ -d "$f" ] && { echo "$f is a directory."; exit 0; }
	[ -L "$f" ] && { echo "$f is a symbolic link."; exit 0; }
	[ -x "$f" ] && { echo "$f is an executeble file."; exit 0; }
}

# make sure filename supplied as command line arg else die
[ $# -eq 0 ] && { echo "Usage: $0 filename"; exit 1; }

# invoke the is_file_dir and pass $file as arg
is_file_dir "$file"