>perl -wE "'a'=~/(a)/; 'a'=~/b/; say $1"
a

>perl -wE "'a'=~/(a)/; 'a'=~/a/; say $1"
Use of uninitialized value $1 in say at -e line 1.


>perl -wE "'a'=~/(a)/; END { say $1 }"
Use of uninitialized value $1 in say at -e line 1.


##</code><code>##

>perl -ne "/^(.*) INFO.+Successfully sent(?{$1})/ }{ print $^R" file