$ perl -E ' $str = q{471234973798375754773971832374974447889743725345932}; say for map { join q{}, ( split m{} )[ 0 .. 9 ] } split m{47}, $str; say for map { substr $_, 0, 10 } split m{47}, $str;' 1234973798 7397183237 8897437253 1234973798 7397183237 8897437253 $