the three assumptions you mentioned are accurate
If you're really sure about the indentation something like that can help : 
use strict;
use warnings;
use v5.10;

my $data = do { local $/; <DATA> };
my @sections = split /(\s{4}pin.*?\s{4}\})/s, $data;
for (@sections)
{
  say;
  say '-' x 24;
}
__END__
  cell (lib_1) {
    dont_use : true ;
    dont_touch : true ;

    pin ("HIZIBI_IN_1") {
      direction : input ;
      clock : true ;
      max_transition : 1 ;
      capacitance : 12 ;
    }  
    pin ("HIZIBI_79")    {
      direction : output ;
      max_transition : 10;
      min_capacitance : 3 ;
    }              
    pin ("HIZIBI_IN_1") {
      direction : input ;
      clock : true ;
      max_transition : 1 ;
      capacitance : 1 ;
    }  
    pin ("HIZIBI_78")    {
      direction : output ;
      max_transition : 10;
      min_capacitance : 34 ;
      capacitance : 34 ;
    }            
    pin ("HIZIBI")    {
      direction : output ;
      clock : true ;
      max_transition : 20;
      related_power_pin : VDD ;
      related_ground_pin : VSS ;
      timing () {
        cell_fall (into_f1) {
          index_1("1,2,3,4,5") ;
          index_2("1,2,3,4,5") ;
          values("13, 13, 14, 16, 18",\
                 "13, 14, 15, 16, 19",\
                 "14, 15, 16, 17, 20",\
                 "15, 15, 16, 18, 20",\
                 "15, 16, 17, 18, 21") ;
        }  
      }  
    }
  }

[download]
It's very rough, and assumes a very consistent indentation. It divides the input into section (even empty ones between the pins but that shouldn't be an issue): 
  cell (lib_1) {
    dont_use : true ;
    dont_touch : true ;


------------------------
    pin ("HIZIBI_IN_1") {
      direction : input ;
      clock : true ;
      max_transition : 1 ;
      capacitance : 12 ;
    }
------------------------


------------------------
    pin ("HIZIBI_79")    {
      direction : output ;
      max_transition : 10;
      min_capacitance : 3 ;
    }
------------------------


------------------------
    pin ("HIZIBI_IN_1") {
      direction : input ;
      clock : true ;
      max_transition : 1 ;
      capacitance : 1 ;
    }
------------------------


------------------------
    pin ("HIZIBI_78")    {
      direction : output ;
      max_transition : 10;
      min_capacitance : 34 ;
      capacitance : 34 ;
    }
------------------------


------------------------
    pin ("HIZIBI")    {
      direction : output ;
      clock : true ;
      max_transition : 20;
      related_power_pin : VDD ;
      related_ground_pin : VSS ;
      timing () {
        cell_fall (into_f1) {
          index_1("1,2,3,4,5") ;
          index_2("1,2,3,4,5") ;
          values("13, 13, 14, 16, 18",\
                 "13, 14, 15, 16, 19",\
                 "14, 15, 16, 17, 20",\
                 "15, 15, 16, 18, 20",\
                 "15, 16, 17, 18, 21") ;
        }
------------------------

      }
    }
  }

------------------------

[download]

Edit: it also assumes that the file is not so big that you can't read it all at once.

In reply to Re^3: Need to save a single line from delete on some special condition by Eily
in thread Need to save a single line from delete on some special condition by anirbanphys

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