>perl -wMstrict -e "my @lines = ( '1. This is just a sample.', '2. This is to check', '3. How a set of values', '4. can be replaced by another', '5. set of values and that too', '6. in the most efficient way.', '99. And also handle large numbers.', '999. Oops, too big!', '99 bottles of beer on the wall does not translate!', ); ;; my %xlate; { my @alphas = (undef, 'a' .. 'zz'); @xlate{ 1 .. $#alphas } = @alphas[ 1 .. $#alphas ]; } ;; s{ \A (\d+) (?= [.]) } { exists $xlate{$1} ? $xlate{$1} : (warn(qq{bad '$1' in '$_'}), '??') }xmse for @lines; ;; print qq{$_\n} for @lines; " bad '999' in '999. Oops, too big!' at -e line 1. a. This is just a sample. b. This is to check c. How a set of values d. can be replaced by another e. set of values and that too f. in the most efficient way. cu. And also handle large numbers. ??. Oops, too big! 99 bottles of beer on the wall does not translate!