Может файл, который был первоначально редок и затем расширенный быть сделанным редким снова?

'perl' решение:

Сценарий:

use warnings;                                                                                                                                                                       
use strict;                                                                                                                                                                         

die "Usage: perl $0 file\n" unless @ARGV == 1;                                                                                                                                      

my (%hash, $region);                                                                                                                                                                

open my $fh, "<", $ARGV[0] or die "Cannot open file $ARGV[0]: $!\n";                                                                                                                

while ( my $line = <$fh> ) {                                                                                                                                                        

        ## Get region, characters until first ':' without spaces at the beginning.                                                                                                  
        $region = $1 if $line =~ /^([^:\s]+)/;                                                                                                                                      

        ## Get names with a regex and save them as keys of a hash, values will be                                                                                                   
        ## regions.                                                                                                                                                                 
        if ( $line =~ /^\s*(?i:groups):\s*\[([^\]]*)\]\s*$/ ) {                                                                                                                     
                my @names = split /,\s*/, $1;                                                                                                                                       
                for my $name ( @names ) {                                                                                                                                           
                        push @{ $hash{ $name } }, $region;                                                                                                                          
                }                                                                                                                                                                   
        }                                                                                                                                                                           
}                                                                                                                                                                                   

## Read names (keys of the hash), open a file for each one and write regions on it.                                                                                                 
for my $name ( sort keys %hash ) {                                                                                                                                                  
        my $outfile = $name . ".txt";                                                                                                                                               
        open my $ofh, ">", $outfile or do { warn "Cannot open $outfile: $!\n"; next };                                                                                              
        print $ofh join( ", ", @{ $hash{ $name } } ), "\n";                                                                                                                         
        close $ofh or warn "Cannot close $outfile\n";                                                                                                                               
}                                                                                                                                                                                   

close $fh or warn "Cannot close $ARGV[0]\n";

Выполнение:

$ perl script.pl infile