how to find and replace using sed code example

Example 1: sed replace in file

sed -i 's/foo/bar/g' hello.txt

Example 2: replace text with sed

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

Example 3: sed replace with variable

Use double quotes to make the shell expand variables while preserving whitespace:

sed -i "s/$var1/ZZ/g" "$file"