Find and Replace using grep and sed

Following command finds all the occurences of <br> in all .xml files in the current directory, and replace those <br> with <br/> . Please note that < and > have been surrounded with [ and ] in the sed command. / in the <br/> tag has been escaped using \. If you want to replace foo with bar, then you can just use those words.

find . -iname "*.xml" | xargs grep -l "<br>" | xargs sed -i -e 's/[<]br[>]/<br\/>/g'

find . -iname "*.xml" | xargs grep -l "<br>" | xargs sed -i -e 's/foo/bar/g'

A more general form of the expression would be

find . \( -name "*.php" -or -name "*.html" \) | xargs grep -l 'TEXT TO SEARCH' | xargs sed -i -e 's/TEXT TO REPLACE/REPLACEMENT STRING/g'