How to validate if the file not passed in - linux

Question

So I have script that takes file from user with option -y or -n and -d is required
script runs ./example.sh -d file -y or -n
variable
file=""
I need to do validation on if the user did not pass file in for example
./example.sh -y --- it should give error "must provide file"`
./example.sh -n --- it should give error "must provide file"`
./example.sh -d --- it should give error "must provide file"
./example.sh -y -n --- it should give error "must provide file"
i came up with this but its not working
#checking if the file is provided
if [ $file -eq 1 ]; then
echo "No file provided"
exit 1
fi
# Does the file exist
which works for checking if the file exists but it only check if the file in there
if [[ ! -f $file ]]; then
echo
echo "Error: The file $file does not exist."
exit 1
fi

Answer 1

Why not simply loop over the arguments and test the -d, -n and -y options in a case statement. The filename must follow the -d option as I understand it. When the -d option is processed in your case statement check that the next argument holds a filename that exists on the system and is non-empty, if so, set the filename, e.g. filename="${argv[i+1]}".
When you exit the option processing loop, simply test if filename is set and you have your answer.
A short example could be:
#!/bin/bash
argc=$# ## argument count
argv=("$#") ## array holding arguments (argument vector)
filename= ## filename is empty
## loop over all arguments, filename must follow -d
for ((i = 0; i < argc; i++)); do
case "${argv[i]}" in
## file exists and non-empty, set filename to argument
-d ) [ -s "${argv[i+1]}" ] && { filename="${argv[i+1]}"; };;
-n ) # do whatever for option n
;;
-y ) # do whatever for option y
;;
esac
done
[ -n "$filename" ] || { ## check filename set or exit
printf "error: file empty or not readable.\n" >&2
exit 1
}
## valid filename received
printf "file '%s' found - script running.\n" "$filename"
Only if a valid filename is given after the -d option will the script run. Otherwise it will give an error message and exit.
Examples
$ ./process-opts.sh -y -n
error: file empty or not readable.
or
$ ./process-opts.sh -y -d -n
error: file empty or not readable.
Finally
$ ./process-opts.sh -y -d README -n
file 'README' found - script running.
or in any order:
$ ./process-opts.sh -y -n -d README
file 'README' found - script running.