the standard distribution as of Perl 5.005) and Storable (included as
of perl 5.8). Keeping all data as text significantly simplifies matters.
+The v-strings are portable only up to v2147483647 (0x7FFFFFFF), that's
+how far EBCDIC, or more precisely UTF-EBCDIC will go.
+
=head2 Files and Filesystems
Most platforms these days structure files in a hierarchical fashion.
modification timestamp), or one second granularity of any timestamps
(e.g. the FAT filesystem limits the time granularity to two seconds).
+The "inode change timestamp" (the <-C> filetest) may really be the
+"creation timestamp" (which it is not in UNIX).
+
VOS perl can emulate Unix filenames with C</> as path separator. The
native pathname characters greater-than, less-than, number-sign, and
percent-sign are always accepted.
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 assume a text file will end with a newline. They should,
but people forget.
-Do not have two files of the same name with different case, like
-F<test.pl> and F<Test.pl>, as many platforms have case-insensitive
-filenames. Also, try not to have non-word characters (except for C<.>)
-in the names, and keep them to the 8.3 convention, for maximum
-portability, onerous a burden though this may appear.
+Do not have two files or directories of the same name with different
+case, like F<test.pl> and F<Test.pl>, as many platforms have
+case-insensitive (or at least case-forgiving) filenames. Also, try
+not to have non-word characters (except for C<.>) in the names, and
+keep them to the 8.3 convention, for maximum portability, onerous a
+burden though this may appear.
Likewise, when using the AutoSplit module, try to keep your functions to
8.3 naming and case-insensitive conventions; or, at the least,
make it so the resulting files have a unique (case-insensitively)
first 8 characters.
-Whitespace in filenames is tolerated on most systems, but not all.
+Whitespace in filenames is tolerated on most systems, but not all,
+and even on systems where it might be tolerated, some utilities
+might become confused by such whitespace.
+
Many systems (DOS, VMS) cannot have more than one C<.> in their filenames.
Don't assume C<< > >> won't be the first character of a filename.
-Always use C<< < >> explicitly to open a file for reading,
-unless you want the user to be able to specify a pipe open.
+Always use C<< < >> explicitly to open a file for reading, or even
+better, use the three-arg version of open, unless you want the user to
+be able to specify a pipe open.
- open(FILE, "< $existing_file") or die $!;
+ open(FILE, '<', $existing_file) or die $!;
If filenames might use strange characters, it is safest to open it
with C<sysopen> instead of C<open>. C<open> is magic and can
translate characters like C<< > >>, C<< < >>, and C<|>, which may
be the wrong thing to do. (Sometimes, though, it's the right thing.)
+Three-arg open can also help protect against this translation in cases
+where it is undesirable.
+
+Don't use C<:> as a part of a filename since many systems use that for
+their own semantics (MacOS Classic for separating pathname components,
+many networking schemes and utilities for separating the nodename and
+the pathname, and so on). For the same reasons, avoid C<@>, C<;> and
+C<|>.
+
+Don't assume that in pathnames you can collapse two leading slashes
+C<//> into one: some networking and clustering filesystems have special
+semantics for that. Let the operating system to sort it out.
+
+The I<portable filename characters> as defined by ANSI C are
+
+ a b c d e f g h i j k l m n o p q r t u v w x y z
+ A B C D E F G H I J K L M N O P Q R T U V W X Y Z
+ 0 1 2 3 4 5 6 7 8 9
+ . _ -
+
+and the "-" shouldn't be the first character. If you want to be
+hypercorrect, stay case-insensitive and within the 8.3 naming
+convention (all the files and directories have to be unique within one
+directory if their names are lowercased and truncated to eight
+characters before the C<.>, if any, and to three characters after the
+C<.>, if any). (And do not use C<.>s in directory names.)
=head2 System Interaction
=head2 Character sets and character encoding
-Assume little about character sets. Assume nothing about
-numerical values (C<ord>, C<chr>) of characters. Do not
-assume that the alphabetic characters are encoded contiguously (in
-the numeric sense). Do not assume anything about the ordering of the
-characters. The lowercase letters may come before or after the
-uppercase letters; the lowercase and uppercase may be interlaced so
-that both `a' and `A' come before `b'; the accented and other
-international characters may be interlaced so that E<auml> comes
-before `b'.
+Assume very little about character sets.
+
+Assume nothing about numerical values (C<ord>, C<chr>) of characters.
+Do not use explicit code point ranges (like \xHH-\xHH); use for
+example symbolic character classes like C<[:print:]>.
+
+Do not assume that the alphabetic characters are encoded contiguously
+(in the numeric sense). There may be gaps.
+
+Do not assume anything about the ordering of the characters.
+The lowercase letters may come before or after the uppercase letters;
+the lowercase and uppercase may be interlaced so that both `a' and `A'
+come before `b'; the accented and other international characters may
+be interlaced so that E<auml> comes before `b'.
=head2 Internationalisation
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<$)>) to work
+for switching identities (or memberships).
+
+Don't assume set-uid and set-gid semantics. (And even if you do,
+think twice: set-uid and set-gid are a known can of security worms.)
+
=head2 Style
For those times when it is necessary to have platform-specific code,
--------------------------------------------
AIX aix aix
BSD/OS bsdos i386-bsdos
+ Darwin darwin darwin
dgux dgux AViiON-dgux
DYNIX/ptx dynixptx i386-dynixptx
FreeBSD freebsd freebsd-i386
Access permissions are mapped onto VOS access-control list changes. (VOS)
+The actual permissions set depend on the value of the C<CYGWIN>
+in the SYSTEM environment settings. (Cygwin)
+
=item chown LIST
Not implemented. (S<Mac OS>, Win32, Plan9, S<RISC OS>, VOS)
Does not automatically flush output handles on some platforms.
(SunOS, Solaris, HP-UX)
+=item exit EXPR
+
+=item exit
+
+Emulates UNIX exit() (which considers C<exit 1> to indicate an error) by
+mapping the C<1> to SS$_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$_NORMAL
+(C<1>); this mapping cannot be overridden. Any other argument to exit()
+is used directly as Perl's exit status. (VMS)
+
=item fcntl FILEHANDLE,FUNCTION,SCALAR
Not implemented. (Win32, VMS)
Not implemented. (Plan9, Win32)
-=item exit EXPR
-
-=item exit
-
-Emulates UNIX exit() (which considers C<exit 1> to indicate an error) by
-mapping the C<1> to SS$_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$_NORMAL
-(C<1>); this mapping cannot be overridden. Any other argument to exit()
-is used directly as Perl's exit status. (VMS)
-
=item getsockopt SOCKET,LEVEL,OPTNAME
Not implemented. (Plan9)
=item select RBITS,WBITS,EBITS,TIMEOUT
-Only implemented on sockets. (Win32)
+Only implemented on sockets. (Win32, VMS)
Only reliable on sockets. (S<RISC OS>)
-Note that the C<socket FILEHANDLE> form is generally portable.
+Note that the C<select FILEHANDLE> form is generally portable.
=item semctl ID,SEMNUM,CMD,ARG
'not numeric' warnings.
mtime and atime are the same thing, and ctime is creation time instead of
-inode change time. (S<Mac OS>)
+inode change time. (S<Mac OS>).
+
+ctime not supported on UFS (S<Mac OS X>).
+
+ctime is creation time instead of inode change time (Win32).
device and inode are not meaningful. (Win32)
=item system LIST
+In general, do not assume the UNIX/POSIX semantics that you can shift
+C<$?> 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
=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
Larry Moore <ljmoore@freespace.net>,
Paul Moore <Paul.Moore@uk.origin-it.com>,
Chris Nandor <pudge@pobox.com>,
-Matthias Neeracher <neeri@iis.ee.ethz.ch>,
+Matthias Neeracher <neeracher@mac.com>,
Philip Newton <pne@cpan.org>,
Gary Ng <71564.1743@CompuServe.COM>,
Tom Phoenix <rootbeer@teleport.com>,
Dan Sugalski <dan@sidhe.org>,
Nathan Torkington <gnat@frii.com>.
-=head1 VERSION
-
-Version 1.50, last modified 10 Jul 2001
projects / p5sagit/p5-mst-13.2.git / blobdiff