Create a bash shell script(1)

cat file.sh

#!/bin/bash
# file.sh: a sample shell script to demonstrate the concept of Bash shell functions
# define usage function
usage(){
    echo "Usage: $0 filename"
    exit 1
}
 
# define is_file_exits function
# $f -> store argument passed to the script
is_file_exits(){
    local f="$1"
    [[ -f "$f" ]] && return 0 || return 1
}
# invoke  usage
# call usage() function if filename not supplied
[[ $# -eq 0 ]] && usage
 
# Invoke is_file_exits
if ( is_file_exits "$1" )
then
 echo "File found"
else
 echo "File not found"
fi

 

Run it as allows:

chomod +x file.sh

./file.sh

./file.sh filename