This is a classic case for use of a flag variable.

# init variable to show we're not in the blcok
my $in_block = 0;

while ( <> ) # process line by line
{
    $in_block = 1 if /^head/; # test for start of block and
                              # set flag true if needed
    print if $in_block; # print if we're in the block
    $in_block = 0 if /tail$/; # test for end of block and
                              # set flag false if needed
}
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Sorry if I misunderstood your question, but according to the way I read it I think this is close. Given this file:

fvewvwef vfewejmnvwev evfjerwvnrevjwe
wervkjvwe wevrjvrenwvr head
vfjlevnerojvnerve
head refejrverjvnerjovnerojvn ercjncer
rljnelrkvnervervekjnve tail fknvbekjev
nweclkneclknerclkernclenelrknclencekn
cwlknelcnlcwnejnrjnrjcnjcncjncnccjn tail
vjenvlejnvlejnrvlejnvejnvejnvejnvejvnejv
head efcjonecjnercjnerjcnerjnc
crjencerjncejlrcn
tail
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I get this output:

head refejrverjvnerjovnerojvn ercjncer
rljnelrkvnervervekjnve tail fknvbekjev
nweclkneclknerclkernclenelrknclencekn
cwlknelcnlcwnejnrjnrjcnjcncjncnccjn tail
head efcjonecjnercjnerjcnerjnc
crjencerjncejlrcn
tail
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Sometimes a simple procedural style works really well, even if you have bells and whistles available. This could be written the same in almost any language. Perl just makes it easier.