use strict;
use warnings;

my $file="test_file.txt";
my $StrSearch = "calendar: Calendar_1_test";
open TEST, $file;

open OUT,">result.txt";

while (<TEST>) {
  if (/$StrSearch/) {
    print OUT;
    while (<TEST>){
      if (/^calendar/){
        last;
      } else {
        print OUT;
      }
    }
  }
}
close TEST;
close OUT;