Substitute a text only in files where it appears

For example, to substitute foo with bar

for f in `grep -lR foo`; do
  echo -n ">> $f";
  sed 's/foo/bar/g' $f > $f.2;
  mv $f.2 $f;
  echo " done.";
done

• for loops on all files containing the text “foo”, grep -l only show the file name with corresponding text inside.
• sed replace foo with bar in all file
• mv save the modification (delete if you don’t want to overwrite the original files, the modified files is named with .2 at the end)