use strict;
print scalar <DATA>;    # print first #PLOT1

while (<DATA>) {
    chomp;              # get rid of EOL
    print /#PLOT/ ? "\n$_\n" : "$_ ";
} ## end while (<DATA>)

__DATA__
#PLOT1
a b c d f g i
a c g s h
b h f d
#PLOT2
b g d i s e
w d u
b a o
n i o p w q c u s t r r y
#PLOT3
e r t d v g
v g b


##</code><code>##

#PLOT1
a b c d f g i a c g s h b h f d 
#PLOT2
b g d i s e w d u b a o n i o p w q c u s t r r y 
#PLOT3
e r t d v g v g b