replace string in a file in linux code example

Example 1: how to find and replace a string in a file using shell script

# 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

Example 2: linux replace string in all files

sed -i 's/old-text/new-text/g' input.txt