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in reply to Re (chip): Two-arg open() considered dangerous
in thread Two-arg open() considered dangerous

It is not guaranteed. From 'perldoc -f sysopen' on 5.005_03 I get:
=item sysopen FILEHANDLE,FILENAME,MODE =item sysopen FILEHANDLE,FILENAME,MODE,PERMS [ snip ] 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.
So those values probably work. But not always.