You could also use the range (flip-flop) operator. The sample below will print lines from the line which starts with "head" (^ anchors to the start) to the one which ends with "tail" (\s*$ allows some white space after tail.)
#!/usr/bin/perl
use strict;
use warnings;
while(<DATA>)
{
print if /^head/i../tail\s*$/i;
}
__DATA__
HEAD gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla tail gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus head bla bla gugus gugus tail
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus head
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
tail gugus gugus
Output
HEAD gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla tail gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus gugus bla bla gugus gugus
bla bla gugus head bla bla gugus gugus tail
Update
If you have the camel book, you can find a discussion on this starting on page 90 (2nd Edition).