#!/usr/bin/perl -w
use strict;

my @lines;
        
while (<DATA>) 
{            
   chomp;
   next if /^\s*$/;

   my ($date, $err_no, $err_msg) = 
       m{\[(.*)\]\s+\[(.*)\]\s+ERRORMSG\s+(.*)};
   
   if (defined $err_msg)  # the match "worked"!
   {                   
      push @lines, $date.' === '.$err_no.' === '.$err_msg."\n";
   }    
   else
   { 
      $lines[@lines-1] =~ s|\n$| $_\n|;
   } 
}      

print @lines;

=prints
2012/02/16 00:08:34 === 29 === unknown error Can't insert into price table Please check Valueprice.pm line 52.
2012/02/16 00:08:34 === 39 === Invalid User
2012/02/16 00:14:52 === 105 === missing conversion rate
2012/02/16 00:14:52 === 29 === Can't use an undefined value as a HASH reference at Value.pm line 77. 
=cut

__DATA__
[2012/02/16 00:08:34] [29] ERRORMSG unknown error Can't insert into price table
Please check
Valueprice.pm line 52.
[2012/02/16 00:08:34] [39] ERRORMSG Invalid User
[2012/02/16 00:14:52] [105] ERRORMSG missing conversion rate
[2012/02/16 00:14:52] [29] ERRORMSG Can't use an undefined value as a HASH reference at Value.pm line 77.