At some stage, I extract some text with Action>Extract and Converters>Advanced extract. My extract result is like this: $1 is a day of the month $2 is a month I want to generate a date like "10-22". So my output expression is $2-$1. But this gives 10-8 10-9 10-10 10-11 ... In fact, I prefer to format all numbers to 2 digits, ...