Like Smaug, I am not sure why you would want to do this. Trying to do it via a single sysopen is going to be affected by the umask as reasonablekeith points out but you could do it within your script like this

use strict;
use warnings;

my $newFile = q{spw585219.txt};
my $newFH;

open $newFH, q{>}, $newFile
   or die qq{open: $newFile: $!\n};
close $newFH
   or die qq{close: $newFile: $!\n};

my $ls = `/usr/bin/ls -l $newFile`;
print $ls;

chmod 0777, $newFile
   or die qq{chmod: $newFile: $!\n};

$ls = `/usr/bin/ls -l $newFile`;
print $ls;

open $newFH, q{>}, $newFile
   or die qq{open: $newFile: $!\n};

print $newFH qq{The quick brown fox etc\n};

close $newFH
   or die qq{close: $newFile: $!\n};

$ls = `/usr/bin/ls -l $newFile`;
print $ls;
[download]

and here is the output showing the ls -l results

-rw-r--r--   1 johngg   staff          0 Nov 21 10:29 spw585219.txt
-rwxrwxrwx   1 johngg   staff          0 Nov 21 10:29 spw585219.txt
-rwxrwxrwx   1 johngg   staff         24 Nov 21 10:29 spw585219.txt
[download]

I hope this is of use.

Cheers,

JohnGG