grep -il '<String>' `find . -name '*.php' -print`
find . -name '*.php' -print0 | xargs -0 grep -il '<String>'

или

find . -name '*.php' -exec grep -il '<String>' {} \; | more
find . -type f -mtime -1 -ls
find . -user <потребител> -mtime 1 > last24.txt
find . -type f -size +100M