How to extract the RegExp matched digit and take it as a variable?

Hi experts,

    I now have a matched pattern like  comPat1=pcreCompile("[_][0-9]$") but I want to extract the number as a variable and 

add one on it (e.g. "_1 " -> "_2", "_2" -> "_3", etc.). How can I do this? I didn't find any related function in PERC/Rex functions.

Is there any way to do this?

Thank you in advance. 

Best Regards,