separator, or go native and use C<.> for path separator and C<:> to
signal filesystems and disk names.
+Don't assume UNIX filesystem access semantics: that read, write,
+and execute are all the permissions there are, and even if they exist,
+that their semantics (for example what do r, w, and x mean on
+a directory) are the UNIX ones. The various UNIX/POSIX compatibility
+layers usually try to make interfaces like chmod() work, but sometimes
+there simply is no good mapping.
+
If all this is intimidating, have no (well, maybe only a little)
fear. There are modules that can help. The File::Spec modules
provide methods to do the Right Thing on whatever platform happens
Don't open the same file more than once at a time for writing, as some
operating systems put mandatory locks on such files.
+Don't assume that write/modify permission on a directory gives the
+right to add or delete files/directories in that directory. That is
+filesystem specific: in some filesystems you need write/modify
+permission also (or even just) in the file/directory itself. In some
+filesystems (AFS, DFS) the permission to add/delete directory entries
+is a completely separate permission.
+
+Don't assume that a single C<unlink> completely gets rid of the file:
+some filesystems (most notably the ones in VMS) have versioned
+filesystems, and unlink() removes only the most recent one (it doesn't
+remove all the versions because by default the native tools on those
+platforms remove just the most recent version, too). The portable
+idiom to remove all the versions of a file is
+
+ 1 while unlink "file";
+
+This will terminate if the file is undeleteable for some reason
+(protected, not there, and so on).
+
Don't count on a specific environment variable existing in C<%ENV>.
Don't count on C<%ENV> entries being case-sensitive, or even
case-preserving. Don't try to clear %ENV by saying C<%ENV = ();>, or,
The Unix System V IPC (C<msg*(), sem*(), shm*()>) is not available
even on all Unix platforms.
+Do not use either the bare result of C<pack("N", 10, 20, 30, 40)> or
+bare v-strings (such as C<v10.20.30.40>) to represent IPv4 addresses:
+both forms just pack the four bytes into network order. That this
+would be equal to the C language C<in_addr> struct (which is what the
+socket code internally uses) is not guaranteed. To be portable use
+the routines of the Socket extension, such as C<inet_aton()>,
+C<inet_ntoa()>, and C<sockaddr_in()>.
+
The rule of thumb for portable code is: Do it all in portable Perl, or
use a module (that may internally implement it with platform-specific
code, but expose a common interface).
Most multi-user platforms provide basic levels of security, usually
implemented at the filesystem level. Some, however, do
-not--unfortunately. Thus the notion of user id, or "home" directory,
+not-- unfortunately. Thus the notion of user id, or "home" directory,
or even the state of being logged-in, may be unrecognizable on many
platforms. If you write programs that are security-conscious, it
is usually best to know what type of system you will be running
under so that you can write code explicitly for that platform (or
class of platforms).
+Don't assume the UNIX filesystem access semantics: the operating
+system or the filesystem may be using some ACL systems, which are
+richer languages than the usual rwx. Even if the rwx exist,
+their semantics might be different.
+
+(From security viewpoint testing for permissions before attempting to
+do something is silly anyway: if one tries this, there is potential
+for race conditions-- someone or something might change the
+permissions between the permissions check and the actual operation.
+Just try the operation.)
+
+Don't assume the UNIX user and group semantics: especially, don't
+expect the C<< $< >> and C<< $> >> (or the C<$(> and C<$)>) to work
+for switching identities (or memberships).
+
+Don't assume set-uid and set-gid semantics. (And even if you do,
+think twice: set-uid and set-gid are a known can of security worms.)
+
=head2 Style
For those times when it is necessary to have platform-specific code,
programs to aid in the testing, or when (as noted above) the tests
assume certain things about the filesystem and paths. Be careful
not to depend on a specific output style for errors, such as when
-checking C<$!> after an system call. Some platforms expect a certain
+checking C<$!> after a system call. Some platforms expect a certain
output format, and perl on those platforms may have been adjusted
accordingly. Most specifically, don't anchor a regex when testing
an error value.
The C<$^O> variable and the C<$Config{archname}> values for various
DOSish perls are as follows:
- OS $^O $Config{'archname'}
- --------------------------------------------
- MS-DOS dos
- PC-DOS dos
- OS/2 os2
- Windows 95 MSWin32 MSWin32-x86
- Windows 98 MSWin32 MSWin32-x86
- Windows NT MSWin32 MSWin32-x86
- Windows NT MSWin32 MSWin32-ALPHA
- Windows NT MSWin32 MSWin32-ppc
- Cygwin cygwin
+ OS $^O $Config{archname} ID Version
+ --------------------------------------------------------
+ MS-DOS dos ?
+ PC-DOS dos ?
+ OS/2 os2 ?
+ Windows 3.1 ? ? 0 3 01
+ Windows 95 MSWin32 MSWin32-x86 1 4 00
+ Windows 98 MSWin32 MSWin32-x86 1 4 10
+ Windows ME MSWin32 MSWin32-x86 1 ?
+ Windows NT MSWin32 MSWin32-x86 2 4 xx
+ Windows NT MSWin32 MSWin32-ALPHA 2 4 xx
+ Windows NT MSWin32 MSWin32-ppc 2 4 xx
+ Windows 2000 MSWin32 MSWin32-x86 2 5 xx
+ Windows XP MSWin32 MSWin32-x86 2 ?
+ Windows CE MSWin32 ? 3
+ Cygwin cygwin ?
The various MSWin32 Perl's can distinguish the OS they are running on
via the value of the fifth element of the list returned from
Does not automatically flush output handles on some platforms.
(SunOS, Solaris, HP-UX)
+=item exit EXPR
+
+=item exit
+
+Emulates UNIX exit() (which considers C<exit 1> to indicate an error) by
+mapping the C<1> to SS$_ABORT (C<44>). This behavior may be overridden
+with the pragma C<use vmsish 'exit'>. As with the CRTL's exit()
+function, C<exit 0> is also mapped to an exit status of SS$_NORMAL
+(C<1>); this mapping cannot be overridden. Any other argument to exit()
+is used directly as Perl's exit status. (VMS)
+
=item fcntl FILEHANDLE,FUNCTION,SCALAR
Not implemented. (Win32, VMS)
=item getsockopt SOCKET,LEVEL,OPTNAME
-Not implemented. (S<Mac OS>, Plan9)
+Not implemented. (Plan9)
=item glob EXPR
=item select RBITS,WBITS,EBITS,TIMEOUT
-Only implemented on sockets. (Win32)
+Only implemented on sockets. (Win32, VMS)
Only reliable on sockets. (S<RISC OS>)
-Note that the C<socket FILEHANDLE> form is generally portable.
+Note that the C<select FILEHANDLE> form is generally portable.
=item semctl ID,SEMNUM,CMD,ARG
=item setsockopt SOCKET,LEVEL,OPTNAME,OPTVAL
-Not implemented. (S<Mac OS>, Plan9)
+Not implemented. (Plan9)
=item shmctl ID,CMD,ARG
dev, rdev, blksize, and blocks are not available. inode is not
meaningful and will differ between stat calls on the same file. (os2)
+some versions of cygwin when doing a stat("foo") and if not finding it
+may then attempt to stat("foo.exe") (Cygwin)
+
=item symlink OLDFILE,NEWFILE
Not implemented. (Win32, VMS, S<RISC OS>)
=item system LIST
+In general, do not assume the UNIX/POSIX semantics that you can shift
+C<$?> right by eight to get the exit value, or that C<$? & 127>
+would give you the number of the signal that terminated the program,
+or that C<$? & 128> would test true if the program was terminated by a
+coredump. Instead, use the POSIX W*() interfaces: for example, use
+WIFEXITED($?) an WEXITVALUE($?) to test for a normal exit and the exit
+value, and WIFSIGNALED($?) and WTERMSIG($?) for a signal exit and the
+signal. Core dumping is not a portable concept, so there's no portable
+way to test for that.
+
Only implemented if ToolServer is installed. (S<Mac OS>)
As an optimization, may not call the command shell specified in
Does not automatically flush output handles on some platforms.
(SunOS, Solaris, HP-UX)
+The return value is POSIX-like (shifted up by 8 bits), which only allows
+room for a made-up value derived from the severity bits of the native
+32-bit condition code (unless overridden by C<use vmsish 'status'>).
+For more details see L<perlvms/$?>. (VMS)
+
=item times
Only the first entry returned is nonzero. (S<Mac OS>)
Truncation to zero-length only. (VOS)
If a FILEHANDLE is supplied, it must be writable and opened in append
-mode (i.e., use C<open(FH, '>>filename')>
+mode (i.e., use C<<< open(FH, '>>filename') >>>
or C<sysopen(FH,...,O_APPEND|O_RDWR)>. If a filename is supplied, it
should not be held open elsewhere. (Win32)
=item utime LIST
-Only the modification time is updated. (S<Mac OS>, VMS, S<RISC OS>)
+Only the modification time is updated. (S<BeOS>, S<Mac OS>, VMS, S<RISC OS>)
May not behave as expected. Behavior depends on the C runtime
library's implementation of utime(), and the filesystem being
As of early 2001 (the Perl releases 5.6.1 and 5.7.1), the following
platforms are able to build Perl from the standard source code
-distribution available at http://www.perl.com/CPAN/src/index.html
+distribution available at http://www.cpan.org/src/index.html
AIX
AmigaOS
Netware
The following platforms have their own source code distributions and
-binaries available via http://www.perl.com/CPAN/ports/index.html:
+binaries available via http://www.cpan.org/ports/index.html:
Perl release
Tandem Guardian 5.004
The following platforms have only binaries available via
-http://www.perl.com/CPAN/ports/index.html :
+http://www.cpan.org/ports/index.html :
Perl release
Although we do suggest that you always build your own Perl from
the source code, both for maximal configurability and for security,
in case you are in a hurry you can check
-http://www.perl.com/CPAN/ports/index.html for binary distributions.
+http://www.cpan.org/ports/index.html for binary distributions.
=head1 SEE ALSO
L<perlaix>, L<perlapollo>, L<perlamiga>, L<perlbeos>, L<perlbs200>,
-L<perlcygwin>, L<perldgux>, L<perldos>, L<perlepoc>, L<perlebcdic>,
+L<perlce>, L<perlcygwin>, L<perldgux>, L<perldos>, L<perlepoc>, L<perlebcdic>,
L<perlhurd>, L<perlhpux>, L<perlmachten>, L<perlmacos>, L<perlmint>,
L<perlmpeix>, L<perlnetware>, L<perlos2>, L<perlos390>, L<perlplan9>,
L<perlqnx>, L<perlsolaris>, L<perltru64>, L<perlunicode>,
Paul Moore <Paul.Moore@uk.origin-it.com>,
Chris Nandor <pudge@pobox.com>,
Matthias Neeracher <neeri@iis.ee.ethz.ch>,
+Philip Newton <pne@cpan.org>,
Gary Ng <71564.1743@CompuServe.COM>,
Tom Phoenix <rootbeer@teleport.com>,
AndrE<eacute> Pirard <A.Pirard@ulg.ac.be>,
projects / p5sagit/p5-mst-13.2.git / blobdiff