This appears to work correctly. Tested with four files.

#!/usr/bin/perl
use warnings;
use strict;

@ARGV > 1 or die "usage: $0  <<MAIN_LIB_FILE>>  <<LIB_FILE_FOR_MARGE>>
+\n\n";

open my $OUT, '>', 'final_file.dat' or die "Cannot open 'final_file.da
+t' because: $!";

while ( <> ) {
    if ( /^\}$/ .. /^\s+.*\{$/ ) {
        print $OUT $_ if /^\s+.*\{$/;
        next;
        }
    print $OUT $_;
    }
print $OUT "}\n";
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