how to find and replace a string in a file using shell script on mac code example

Example: how to find and replace a string in a file using shell script on mac

# replaces ALL(g i.e. global) ouccurences of "original_string" with "new_string", 
# in the file file_name.ext_name
sed -i '' "s/original_string/new_string/g" file_name.ext_name