I got a flip flop one for ya

#generator
perl -le " print qq,line $_, for 1..100 "

#the proggie (prints the 6th line after /line 1/ is detected
perl -ne " /line 1/ ..  $a++ == 6 && print "

# sample run
perl -le " print qq,line $_, for 1..100 " | perl -ne " /line 1/ ..  $a
+++ == 6 && print "

#yields
line 7
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