13:41 >perl -wE "say qq[Matched >$1<] if qq[abc2345] =~ /([0-9]+)\s/;

13:41 >perl -wE "say qq[Matched >$1<] if qq[abc2345 ] =~ /([0-9]+)\s/;
Matched >2345<

13:42 >perl -wE "say qq[Matched >$1<] if qq[abc2345\n] =~ /([0-9]+)\s/;
Matched >2345<

13:42 >perl -v

This is perl 5, version 26, subversion 0 (v5.26.0) built for MSWin32-x64-multi-thread-ld