how to replace cirtain string in file linux code example

Example 1: linux replace string in all files

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

Example 2: sed replace in file

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

Example 3: bash find and replace all files with specifc name with another file

find . -name "boom.txt" -exec cp ~/replace.txt {} \;