Shell Programming and Scripting

bash-3.2$ cat null_status_of_parameters.sh
#!/bin/sh
#WASS that takes Search String & File Name from the terminal and check for Null Status. If either is NULL then pgm should quit.
echo "Please Enter the Search String:"
read pat
if [ -Z $pat ]
  then
     echo "Pattern entered is Empty"
     exit
  else
       echo "Please enter the File name:"
       read file
     if [ -Z $file ]
        then
           echo "File name not passed"
           exit
        else
           echo "Following is the grepped output:"
           grep $pat $file
      fi
fi
bash-3.2$

bash-3.2$ ./null_status_of_parameters.sh
Please Enter the Search String:
Manish
./null_status_of_parameters.sh: line 8: [: -Z: unary operator expected
Please enter the File name:
text_file
./null_status_of_parameters.sh: line 15: [: -Z: unary operator expected

Hi all.... I am Manish, I am learning UNIX.
bash-3.2$

if [ -z $pat ]