perl -de "$s=qq(1a2a3a4a5a); if ($s=~/(\d+)/){print $1};"
Default die handler restored.

Loading DB routines from perl5db.pl version 1.07
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   $s=qq(1a2a3a4a5a); if ($s=~/(\d+)/){print $1};
  DB<1> n
main::(-e:1):   $s=qq(1a2a3a4a5a); if ($s=~/(\d+)/){print $1};
  DB<1> p $_

  DB<2>