=over

=item sysopen FILEHANDLE,FILENAME,MODE

=item sysopen FILEHANDLE,FILENAME,MODE,PERMS

Opens the file whose filename is given by FILENAME, and associates it
with FILEHANDLE.  If FILEHANDLE is an expression, its value is used as
the name of the real filehandle wanted.  This function calls the
underlying operating system's C<open()> function with the parameters
FILENAME, MODE, PERMS.

The possible values and flag bits of the MODE parameter are
system-dependent; they are available via the standard module C<Fcntl>.
For historical reasons, some values work on almost every system
supported by perl: zero means read-only, one means write-only, and two
means read/write.  We know that these values do I<not> work under
OS/390 & VM/ESA Unix and on the Macintosh; you probably don't want to
use them in new code.

If the file named by FILENAME does not exist and the C<open()> call creates
it (typically because MODE includes the C<O_CREAT> flag), then the value of
PERMS specifies the permissions of the newly created file.  If you omit
the PERMS argument to C<sysopen()>, Perl uses the octal value C<0666>.
These permission values need to be in octal, and are modified by your
process's current C<umask>.

You should seldom if ever use C<0644> as argument to C<sysopen()>, because
that takes away the user's option to have a more permissive umask.
Better to omit it.  See the perlfunc(1) entry on C<umask> for more
on this.

See L<perlopentut> for a kinder, gentler explanation of opening files.

=back