FILE2

AAA
  text1
  text2
  text3
EOAAA

BBB
  text4
EOBBB

CCC
  text5
  text6
  text7
  text8
EOCCC
##</code><code>##

FILE1

SEGMENT1
  text1
  text2
  text3
EOS1

SEGMENT2
  text4
EOS2

SEGMENT3
  text5
  text6
  text7
  text8
##</code><code>##

FILE3

P201
  text1
  text2
  text3
EOP201

P333
  text4
EOP333

P588
  text5
  text6
  text7
  text8
EOP588
##</code><code>##

use strict;
my @jobs = (
      'file2.txt|AAA|EOAAA',
      'file1.txt|SEGMENT3|EOS3',
      'file3.txt|P333|EOP333'
);

for (@jobs) {
   my ($file, $beg, $end) = split /\|/;
   my $first_line = 1;
   my @lines = ();
   print "Opening file: '$file'\n",
         "   beg:   '$beg'   end:   '$end'\n";
   open (INFILE, "<$file")
      or die "Could not open '$file': $!\n";
   while (<INFILE>) {
      if (/$beg/ .. /$end/) {
         chomp;
         print "   first: '$_'\n\n" if $first_line;
         $first_line = 0;
         push (@lines, $_);
      }
   }
   print "$_\n" for @lines;
   print "-" x 30, "\n\n";
   undef @lines;
}
##</code><code>##

Opening file: 'file2.txt'
   beg:   'AAA'   end:   'EOAAA'
   first: 'AAA'

AAA
  text1
  text2
  text3
EOAAA
------------------------------

Opening file: 'file1.txt'
   beg:   'SEGMENT3'   end:   'EOS3'
   first: 'SEGMENT3'

SEGMENT3
  text5
  text6
  text7
  text8
------------------------------

Opening file: 'file3.txt'
   beg:   'P333'   end:   'EOP333'
   first: 'FILE3'

FILE3

P201
  text1
  text2
  text3
EOP201

P333
  text4
EOP333
------------------------------
##</code><code>##

if ((/$beg/ .. /$end/) or (/$beg/ .. eof())) {