Am facing with this part of code especially change file,rename file and write file subroutine

sub rename_dirs {
    my ( $top_dir, $name_map, $regex ) = @_;
    

    opendir (my $dh, $top_dir) or die "Can't open $top_dir: $!";
    my $save_dir = getcwd();
    chdir $top_dir;
    while (my $name = readdir $dh) {

        next if ($name eq '.') or ($name eq '..'); 
        if ( ( -d $name ) && ( exists $name_map->{$name} ) ) {
            print $name;
            my $new_name = $name_map->{$name};
            #print $new_name;
            rename_file_or_dir( $name, $new_name );
            $name = $new_name;
            
            #print $name;
        }
        elsif ( -f $name ) {
            if (( my $base_name = $name) =~ s/\.config$// ) {
                if ( $name_map->{$base_name} ) {
                    my $new_name = $name_map->{$base_name} . '.config'
+;
                  #  print $new_name;
                    rename_file_or_dir( $name, $new_name );
                    change_file( $new_name, $name_map, $regex );
                }
            }
        }
        rename_dirs( $name, $name_map, $regex ) if -d $name;
    }
    chdir $save_dir;
}

sub change_file {
    my ( $fn, $map, $regex ) = @_;
   # print $fn;

    open ( my $fh, '<', $fn ) or die "Could not open file '$fn': $!";
    my $str = do { local $/; <$fh> };
    print $str;
    close $fh;
    my $num_replacements = $str =~ s/($regex)/$map->{$1}/ge;

    if ( $num_replacements ) {
        write_new_file( $fn, \$str );
    }
}

sub write_new_file {
    my ( $fn, $str ) = @_;

    open ( my $fh, '>', $fn ) or die "Could not open file '$fn': $!";
    print $fh $str;
    close $fh;
}

sub rename_file_or_dir {
    my ( $name, $new_name ) = @_;
    File::Copy::move( $name, $new_name )
        or die "Could not rename '$name' as '$new_name': $!";
}

sub read_map {
    my ( $fn ) = @_;

    my %name_map;

    open( my $fh, '<', $fn ) or die "Could not open file '$fn': $!";
    while( my $line = <$fh> ) {
        chomp $line;
        my @fields = split /:/, $line;
       # print @fields;
        if ( @fields == 3 ) {
            $name_map{$fields[2]} = $fields[1];
        }
    }
    close $fh;
    return \%name_map;
}
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