For example, to substitute foo with bar

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

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