Script to search and replace a string in a file using awk

To search and replace a string we use the following syntax with awk:
awk '{ gsub(/SearchString/, ReplaceString); print }'

Script, to enter a filename, search and replace the string in the file:

echo -n "Enter Filename: "  
read file  
echo -n "Enter Search String: "  
read searchstr  
echo -n "Enter String to replace with: "  
read replacestr  
cat $file | awk -v var2=$replacestr '{ gsub(/'$searchstr'/,var2); print}' > file.tmp  
rm -rf $file  
mv file.tmp $file