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


# de(clare|fine) variables:
my $filename = 'my.file';

# set mask for "readable only by user who runs this script":
umask 077;

# create a file with perms defined by above mask:
open (FH, ">$filename") or die "Error opening $filename: $!";
print FH "foo\n";
close FH or die "Error closing $filename: $!";