X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/c40b5d1d4ac4304e78466da597926abb31c7b9e5..aa6f04ce06ca4e673f605bf3d01a6e8d65f6fbb2:/pod/perlport.pod diff --git a/pod/perlport.pod b/pod/perlport.pod index 7ec2309..9c3005e 100644 --- a/pod/perlport.pod +++ b/pod/perlport.pod @@ -59,7 +59,7 @@ choices you can avail yourself of, and at the same time you can give your users lots of platform choices. On the other hand, when you have to take advantage of some unique feature of a particular platform, as is often the case with systems programming (whether for Unix, Windows, -S, VMS, etc.), consider writing platform-specific code. +VMS, etc.), consider writing platform-specific code. When the code will run on only two or three operating systems, you may need to consider only the differences of those particular systems. @@ -67,9 +67,9 @@ The important thing is to decide where the code will run and to be deliberate in your decision. The material below is separated into three main sections: main issues of -portability (L<"ISSUES">, platform-specific issues (L<"PLATFORMS">, and +portability (L<"ISSUES">), platform-specific issues (L<"PLATFORMS">), and built-in perl functions that behave differently on various ports -(L<"FUNCTION IMPLEMENTATIONS">. +(L<"FUNCTION IMPLEMENTATIONS">). This information should not be considered complete; it includes possibly transient information about idiosyncrasies of some of the ports, almost @@ -88,27 +88,15 @@ and S uses C<\015>. Perl uses C<\n> to represent the "logical" newline, where what is logical may depend on the platform in use. In MacPerl, C<\n> always -means C<\015>. In DOSish perls, C<\n> usually means C<\012>, but -when accessing a file in "text" mode, STDIO translates it to (or -from) C<\015\012>, depending on whether you're reading or writing. -Unix does the same thing on ttys in canonical mode. C<\015\012> -is commonly referred to as CRLF. - -A common cause of unportable programs is the misuse of chop() to trim -newlines: - - # XXX UNPORTABLE! - while() { - chop; - @array = split(/:/); - #... - } +means C<\015>. In DOSish perls, C<\n> usually means C<\012>, but when +accessing a file in "text" mode, perl uses the C<:crlf> layer that +translates it to (or from) C<\015\012>, depending on whether you're +reading or writing. Unix does the same thing on ttys in canonical +mode. C<\015\012> is commonly referred to as CRLF. -You can get away with this on Unix and MacOS (they have a single -character end-of-line), but the same program will break under DOSish -perls because you're only chop()ing half the end-of-line. Instead, -chomp() should be used to trim newlines. The Dunce::Files module can -help audit your code for misuses of chop(). +To trim trailing newlines from text lines use chomp(). With default +settings that function looks for a trailing C<\n> character and thus +trims in a portable way. When dealing with binary files (or text files in binary mode) be sure to explicitly set $/ to the appropriate value for your file format @@ -188,12 +176,12 @@ The Unix column assumes that you are not accessing a serial line "\n", and "\n" on output becomes CRLF. These are just the most common definitions of C<\n> and C<\r> in Perl. -There may well be others. For example, on an EBCDIC implementation such -as z/OS or OS/400 the above material is similar to "Unix" but the code -numbers change: +There may well be others. For example, on an EBCDIC implementation +such as z/OS (OS/390) or OS/400 (using the ILE, the PASE is ASCII-based) +the above material is similar to "Unix" but the code numbers change: - LF eq \025 eq \x15 eq chr(21) eq CP-1047 21 - LF eq \045 eq \x25 eq \cU eq chr(37) eq CP-0037 37 + LF eq \025 eq \x15 eq \cU eq chr(21) eq CP-1047 21 + LF eq \045 eq \x25 eq chr(37) eq CP-0037 37 CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-1047 13 CR eq \015 eq \x0D eq \cM eq chr(13) eq CP-0037 13 @@ -224,6 +212,10 @@ them in big-endian mode. To avoid this problem in network (socket) connections use the C and C formats C and C, the "network" orders. These are guaranteed to be portable. +As of perl 5.9.2, you can also use the C> and C> modifiers +to force big- or little-endian byte-order. This is useful if you want +to store signed integers or 64-bit integers, for example. + You can explore the endianness of your platform by unpacking a data structure packed in native format such as: @@ -268,7 +260,7 @@ as path separator, or in their own idiosyncratic ways (such as having several root directories and various "unrooted" device files such NIL: and LPT:). -S uses C<:> as a path separator instead of C. +S 9 and earlier used C<:> as a path separator instead of C. The filesystem may support neither hard links (C) nor symbolic links (C, C, C). @@ -279,7 +271,7 @@ 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<-C> filetest) may really be the -"creation timestamp" (which it is not in UNIX). +"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 @@ -289,10 +281,10 @@ S perl can emulate Unix filenames with C as path 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, +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 +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. @@ -303,9 +295,9 @@ to be running the program. use File::Spec::Functions; chdir(updir()); # go up one directory - $file = catfile(curdir(), 'temp', 'file.txt'); + my $file = catfile(curdir(), 'temp', 'file.txt'); # on Unix and Win32, './temp/file.txt' - # on Mac OS, ':temp:file.txt' + # on Mac OS Classic, ':temp:file.txt' # on VMS, '[.temp]file.txt' File::Spec is available in the standard distribution as of version @@ -356,14 +348,15 @@ 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. +Many systems (DOS, VMS ODS-2) 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, 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 my $fh, '<', $existing_file) or die $!; If filenames might use strange characters, it is safest to open it with C instead of C. C is magic and can @@ -373,7 +366,7 @@ Three-arg open can also help protect against this translation in cases where it is undesirable. Don't use C<:> as a part of a filename since many systems use that for -their own semantics (MacOS Classic for separating pathname components, +their own semantics (Mac OS Classic for separating pathname components, many networking schemes and utilities for separating the nodename and the pathname, and so on). For the same reasons, avoid C<@>, C<;> and C<|>. @@ -404,10 +397,12 @@ interaction. A program requiring a command line interface might not work everywhere. This is probably for the user of the program to deal with, so don't stay up late worrying about it. -Some platforms can't delete or rename files held open by the system. -Remember to C files when you are done with them. Don't -C or C an open file. Don't C or C a -file already tied or opened; C or C it first. +Some platforms can't delete or rename files held open by the system, +this limitation may also apply to changing filesystem metainformation +like file permissions or owners. Remember to C files when you +are done with them. Don't C or C an open file. Don't +C or C a file already tied or opened; C or C +it first. Don't open the same file more than once at a time for writing, as some operating systems put mandatory locks on such files. @@ -438,6 +433,16 @@ if you really have to, make it conditional on C<$^O ne 'VMS'> since in VMS the C<%ENV> table is much more than a per-process key-value string table. +On VMS, some entries in the %ENV hash are dynamically created when +their key is used on a read if they did not previously exist. The +values for C<$ENV{HOME}>, C<$ENV{TERM}>, C<$ENV{HOME}>, and C<$ENV{USER}>, +are known to be dynamically generated. The specific names that are +dynamically generated may vary with the version of the C library on VMS, +and more may exist than is documented. + +On VMS by default, changes to the %ENV hash are persistent after the process +exits. This can cause unintended issues. + Don't count on signals or C<%SIG> for anything. Don't count on filename globbing. Use C, C, and @@ -446,7 +451,12 @@ C instead. Don't count on per-program environment variables, or per-program current directories. -Don't count on specific values of C<$!>. +Don't count on specific values of C<$!>, neither numeric nor +especially the strings values. Users may switch their locales causing +error messages to be translated into their languages. If you can +trust a POSIXish environment, you can portably use the symbols defined +by the Errno module, like ENOENT. And don't trust on the values of C<$!> +at all except immediately after a failed system call. =head2 Command names versus file pathnames @@ -469,16 +479,54 @@ file name. To convert $^X to a file pathname, taking account of the requirements of the various operating system possibilities, say: - use Config; - $thisperl = $^X; - if ($^O ne 'VMS') - {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;} + + use Config; + my $thisperl = $^X; + if ($^O ne 'VMS') + {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;} To convert $Config{perlpath} to a file pathname, say: - use Config; - $thisperl = $Config{perlpath}; - if ($^O ne 'VMS') - {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;} + + use Config; + my $thisperl = $Config{perlpath}; + if ($^O ne 'VMS') + {$thisperl .= $Config{_exe} unless $thisperl =~ m/$Config{_exe}$/i;} + +=head2 Networking + +Don't assume that you can reach the public Internet. + +Don't assume that there is only one way to get through firewalls +to the public Internet. + +Don't assume that you can reach outside world through any other port +than 80, or some web proxy. ftp is blocked by many firewalls. + +Don't assume that you can send email by connecting to the local SMTP port. + +Don't assume that you can reach yourself or any node by the name +'localhost'. The same goes for '127.0.0.1'. You will have to try both. + +Don't assume that the host has only one network card, or that it +can't bind to many virtual IP addresses. + +Don't assume a particular network device name. + +Don't assume a particular set of ioctl()s will work. + +Don't assume that you can ping hosts and get replies. + +Don't assume that any particular port (service) will respond. + +Don't assume that Sys::Hostname (or any other API or command) returns +either a fully qualified hostname or a non-qualified hostname: it all +depends on how the system had been configured. Also remember that for +things such as DHCP and NAT, the hostname you get back might not be +very useful. + +All the above "don't":s may look daunting, and they are, but the key +is to degrade gracefully if one cannot reach the particular network +service one wants. Croaking or hanging do not look very professional. =head2 Interprocess Communication (IPC) @@ -564,26 +612,34 @@ work with any DBM module. See L for more details. The system's notion of time of day and calendar date is controlled in widely different ways. Don't assume the timezone is stored in C<$ENV{TZ}>, and even if it is, don't assume that you can control the timezone through -that variable. +that variable. Don't assume anything about the three-letter timezone +abbreviations (for example that MST would be the Mountain Standard Time, +it's been known to stand for Moscow Standard Time). If you need to +use timezones, express them in some unambiguous format like the +exact number of minutes offset from UTC, or the POSIX timezone +format. Don't assume that the epoch starts at 00:00:00, January 1, 1970, -because that is OS- and implementation-specific. It is better to store a date -in an unambiguous representation. The ISO-8601 standard defines -"YYYY-MM-DD" as the date format. A text representation (like "1987-12-18") -can be easily converted into an OS-specific value using a module like -Date::Parse. An array of values, such as those returned by -C, can be converted to an OS-specific representation using -Time::Local. +because that is OS- and implementation-specific. It is better to +store a date in an unambiguous representation. The ISO 8601 standard +defines YYYY-MM-DD as the date format, or YYYY-MM-DDTHH-MM-SS +(that's a literal "T" separating the date from the time). +Please do use the ISO 8601 instead of making us guess what +date 02/03/04 might be. ISO 8601 even sorts nicely as-is. +A text representation (like "1987-12-18") can be easily converted +into an OS-specific value using a module like Date::Parse. +An array of values, such as those returned by C, can be +converted to an OS-specific representation using Time::Local. When calculating specific times, such as for tests in time or date modules, it may be appropriate to calculate an offset for the epoch. require Time::Local; - $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70); + my $offset = Time::Local::timegm(0, 0, 0, 1, 0, 70); -The value for C<$offset> in Unix will be C<0>, but in Mac OS will be -some large number. C<$offset> can then be added to a Unix time value -to get what should be the proper value on any system. +The value for C<$offset> in Unix will be C<0>, but in Mac OS Classic +will be some large number. C<$offset> can then be added to a Unix time +value to get what should be the proper value on any system. =head2 Character sets and character encoding @@ -598,9 +654,9 @@ Do not assume that the alphabetic characters are encoded contiguously 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 comes before `b'. +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 comes before "b". =head2 Internationalisation @@ -611,6 +667,22 @@ or at least more convenient and native-friendly for non-English users. The system affects character sets and encoding, and date and time formatting--amongst other things. +If you really want to be international, you should consider Unicode. +See L and L for more information. + +If you want to use non-ASCII bytes (outside the bytes 0x00..0x7f) in +the "source code" of your code, to be portable you have to be explicit +about what bytes they are. Someone might for example be using your +code under a UTF-8 locale, in which case random native bytes might be +illegal ("Malformed UTF-8 ...") This means that for example embedding +ISO 8859-1 bytes beyond 0x7f into your strings might cause trouble +later. If the bytes are native 8-bit bytes, you can use the C +pragma. If the bytes are in a string (regular expression being a +curious string), you can often also use the C<\xHH> notation instead +of embedding the bytes as-is. (If you want to write your code in UTF-8, +you can use the C.) The C and C pragmata are +available since Perl 5.6.0. + =head2 System Resources If your code is destined for systems with severely constrained (or @@ -621,10 +693,10 @@ of avoiding wasteful constructs such as: for (0..10000000) {} # bad for (my $x = 0; $x <= 10000000; ++$x) {} # good - @lines = ; # bad + my @lines = <$very_large_file>; # bad - while () {$file .= $_} # sometimes bad - $file = join('', ); # better + while (<$fh>) {$file .= $_} # sometimes bad + my $file = join('', <$fh>); # better The last two constructs may appear unintuitive to most people. The first repeatedly grows a string, whereas the second allocates a @@ -634,26 +706,26 @@ more efficient that the first. =head2 Security 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, +implemented at the filesystem level. Some, however, unfortunately do +not. 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 +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 +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 +Don't assume the Unix user and group semantics: especially, don't expect the C<< $< >> and C<< $> >> (or the C<$(> and C<$)>) to work for switching identities (or memberships). @@ -672,12 +744,14 @@ Be careful in the tests you supply with your module or programs. Module code may be fully portable, but its tests might not be. This often happens when tests spawn off other processes or call external programs to aid in the testing, or when (as noted above) the tests -assume certain things about the filesystem and paths. Be careful -not to depend on a specific output style for errors, such as when -checking C<$!> after 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. +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<$!> after a failed system call. Using C<$!> for anything else than +displaying it as output is doubtful (though see the Errno module for +testing reasonably portably for error value). 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. =head1 CPAN Testers @@ -691,11 +765,17 @@ problems in their code that crop up because of lack of testing on other platforms; two, to provide users with information about whether a given module works on a given platform. +Also see: + =over 4 -=item Mailing list: cpan-testers@perl.org +=item * + +Mailing list: cpan-testers-discuss@perl.org + +=item * -=item Testing results: http://testers.cpan.org/ +Testing results: L =back @@ -732,6 +812,7 @@ are a few of the more popular Unix flavors: dgux dgux AViiON-dgux DYNIX/ptx dynixptx i386-dynixptx FreeBSD freebsd freebsd-i386 + Haiku haiku BePC-haiku Linux linux arm-linux Linux linux i386-linux Linux linux i586-linux @@ -739,7 +820,6 @@ are a few of the more popular Unix flavors: HP-UX hpux PA-RISC1.1 IRIX irix irix Mac OS X darwin darwin - MachTen PPC machten powerpc-machten NeXT 3 next next-fat NeXT 4 next OPENSTEP-Mach openbsd openbsd i386-openbsd @@ -766,10 +846,10 @@ Users familiar with I or I style shells should be aware that each of these file specifications may have subtle differences: - $filespec0 = "c:/foo/bar/file.txt"; - $filespec1 = "c:\\foo\\bar\\file.txt"; - $filespec2 = 'c:\foo\bar\file.txt'; - $filespec3 = 'c:\\foo\\bar\\file.txt'; + my $filespec0 = "c:/foo/bar/file.txt"; + my $filespec1 = "c:\\foo\\bar\\file.txt"; + my $filespec2 = 'c:\foo\bar\file.txt'; + my $filespec3 = 'c:\\foo\\bar\\file.txt'; System calls accept either C or C<\> as the path separator. However, many command-line utilities of DOS vintage treat C as @@ -818,10 +898,14 @@ DOSish perls are as follows: Windows NT MSWin32 MSWin32-x86 2 4 xx Windows NT MSWin32 MSWin32-ALPHA 2 4 xx Windows NT MSWin32 MSWin32-ppc 2 4 xx - Windows 2000 MSWin32 MSWin32-x86 2 5 xx - Windows XP MSWin32 MSWin32-x86 2 ? + Windows 2000 MSWin32 MSWin32-x86 2 5 00 + Windows XP MSWin32 MSWin32-x86 2 5 01 + Windows 2003 MSWin32 MSWin32-x86 2 5 02 + Windows Vista MSWin32 MSWin32-x86 2 6 00 + Windows 7 MSWin32 MSWin32-x86 2 6 01 + Windows 7 MSWin32 MSWin32-x64 2 6 01 Windows CE MSWin32 ? 3 - Cygwin cygwin ? + Cygwin cygwin cygwin The various MSWin32 Perl's can distinguish the OS they are running on via the value of the fifth element of the list returned from @@ -832,20 +916,26 @@ Win32::GetOSVersion(). For example: print +('3.1','95','NT')[$os_version_info[4]],"\n"; } +There are also Win32::IsWinNT() and Win32::IsWin95(), try C, +and as of libwin32 0.19 (not part of the core Perl distribution) +Win32::GetOSName(). The very portable POSIX::uname() will work too: + + c:\> perl -MPOSIX -we "print join '|', uname" + Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86 + Also see: =over 4 =item * -The djgpp environment for DOS, http://www.delorie.com/djgpp/ +The djgpp environment for DOS, L and L. =item * The EMX environment for DOS, OS/2, etc. emx@iaehv.nl, -http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or -ftp://hobbes.nmsu.edu/pub/os2/dev/emx/ Also L. +L Also L. =item * @@ -858,17 +948,17 @@ The C modules in L. =item * -The ActiveState Pages, http://www.activestate.com/ +The ActiveState Pages, L =item * The Cygwin environment for Win32; F (installed -as L), http://www.cygwin.com/ +as L), L =item * The U/WIN environment for Win32, -http://www.research.att.com/sw/tools/uwin/ +L =item * @@ -876,88 +966,12 @@ Build instructions for OS/2, L =back -=head2 S - -Any module requiring XS compilation is right out for most people, because -MacPerl is built using non-free (and non-cheap!) compilers. Some XS -modules that can work with MacPerl are built and distributed in binary -form on CPAN. - -Directories are specified as: - - volume:folder:file for absolute pathnames - volume:folder: for absolute pathnames - :folder:file for relative pathnames - :folder: for relative pathnames - :file for relative pathnames - file for relative pathnames - -Files are stored in the directory in alphabetical order. Filenames are -limited to 31 characters, and may include any character except for -null and C<:>, which is reserved as the path separator. - -Instead of C, see C and C in the -Mac::Files module, or C and C. - -In the MacPerl application, you can't run a program from the command line; -programs that expect C<@ARGV> to be populated can be edited with something -like the following, which brings up a dialog box asking for the command -line arguments. - - if (!@ARGV) { - @ARGV = split /\s+/, MacPerl::Ask('Arguments?'); - } - -A MacPerl script saved as a "droplet" will populate C<@ARGV> with the full -pathnames of the files dropped onto the script. - -Mac users can run programs under a type of command line interface -under MPW (Macintosh Programmer's Workshop, a free development -environment from Apple). MacPerl was first introduced as an MPW -tool, and MPW can be used like a shell: - - perl myscript.plx some arguments - -ToolServer is another app from Apple that provides access to MPW tools -from MPW and the MacPerl app, which allows MacPerl programs to use -C, backticks, and piped C. - -"S" is the proper name for the operating system, but the value -in C<$^O> is "MacOS". To determine architecture, version, or whether -the application or MPW tool version is running, check: - - $is_app = $MacPerl::Version =~ /App/; - $is_tool = $MacPerl::Version =~ /MPW/; - ($version) = $MacPerl::Version =~ /^(\S+)/; - $is_ppc = $MacPerl::Architecture eq 'MacPPC'; - $is_68k = $MacPerl::Architecture eq 'Mac68K'; - -S, based on NeXT's OpenStep OS, runs MacPerl natively, under the -"Classic" environment. There is no "Carbon" version of MacPerl to run -under the primary Mac OS X environment. S and its Open Source -version, Darwin, both run Unix perl natively. - -Also see: - -=over 4 - -=item * - -MacPerl Development, http://dev.macperl.org/ . - -=item * - -The MacPerl Pages, http://www.macperl.com/ . - -=item * - -The MacPerl mailing lists, http://lists.perl.org/ . - -=back - =head2 VMS Perl on VMS is discussed in L in the perl distribution. + +The official name of VMS as of this writing is OpenVMS. + Perl on VMS can accept either VMS- or Unix-style file specifications as in either of the following: @@ -994,39 +1008,112 @@ you are so inclined. For example: Do take care with C<$ ASSIGN/nolog/user SYS$COMMAND: SYS$INPUT> if your perl-in-DCL script expects to do things like C<< $read = ; >>. -Filenames are in the format "name.extension;version". The maximum -length for filenames is 39 characters, and the maximum length for +The VMS operating system has two filesystems, known as ODS-2 and ODS-5. + +For ODS-2, filenames are in the format "name.extension;version". The +maximum length for filenames is 39 characters, and the maximum length for extensions is also 39 characters. Version is a number from 1 to 32767. Valid characters are C. -VMS's RMS filesystem is case-insensitive and does not preserve case. -C returns lowercased filenames, but specifying a file for -opening remains case-insensitive. Files without extensions have a -trailing period on them, so doing a C with a file named F -will return F (though that file could be opened with +The ODS-2 filesystem is case-insensitive and does not preserve case. +Perl simulates this by converting all filenames to lowercase internally. + +For ODS-5, filenames may have almost any character in them and can include +Unicode characters. Characters that could be misinterpreted by the DCL +shell or file parsing utilities need to be prefixed with the C<^> +character, or replaced with hexadecimal characters prefixed with the +C<^> character. Such prefixing is only needed with the pathnames are +in VMS format in applications. Programs that can accept the Unix format +of pathnames do not need the escape characters. The maximum length for +filenames is 255 characters. The ODS-5 file system can handle both +a case preserved and a case sensitive mode. + +ODS-5 is only available on the OpenVMS for 64 bit platforms. + +Support for the extended file specifications is being done as optional +settings to preserve backward compatibility with Perl scripts that +assume the previous VMS limitations. + +In general routines on VMS that get a Unix format file specification +should return it in a Unix format, and when they get a VMS format +specification they should return a VMS format unless they are documented +to do a conversion. + +For routines that generate return a file specification, VMS allows setting +if the C library which Perl is built on if it will be returned in VMS +format or in Unix format. + +With the ODS-2 file system, there is not much difference in syntax of +filenames without paths for VMS or Unix. With the extended character +set available with ODS-5 there can be a significant difference. + +Because of this, existing Perl scripts written for VMS were sometimes +treating VMS and Unix filenames interchangeably. Without the extended +character set enabled, this behavior will mostly be maintained for +backwards compatibility. + +When extended characters are enabled with ODS-5, the handling of +Unix formatted file specifications is to that of a Unix system. + +VMS file specifications without extensions have a trailing dot. An +equivalent Unix file specification should not show the trailing dot. + +The result of all of this, is that for VMS, for portable scripts, you +can not depend on Perl to present the filenames in lowercase, to be +case sensitive, and that the filenames could be returned in either +Unix or VMS format. + +And if a routine returns a file specification, unless it is intended to +convert it, it should return it in the same format as it found it. + +C by default has traditionally returned lowercased filenames. +When the ODS-5 support is enabled, it will return the exact case of the +filename on the disk. + +Files without extensions have a trailing period on them, so doing a +C in the default mode with a file named F will +return F when VMS is (though that file could be opened with C). +With support for extended file specifications and if C was +given a Unix format directory, a file named F will return F +and optionally in the exact case on the disk. When C is given +a VMS format directory, then C should return F, and +again with the optionally the exact case. + RMS had an eight level limit on directory depths from any rooted logical -(allowing 16 levels overall) prior to VMS 7.2. Hence -C is a valid directory specification but -C is not. F authors might -have to take this into account, but at least they can refer to the former -as C. +(allowing 16 levels overall) prior to VMS 7.2, and even with versions of +VMS on VAX up through 7.3. Hence C is a +valid directory specification but C is +not. F authors might have to take this into account, but at +least they can refer to the former as C. + +Pumpkings and module integrators can easily see whether files with too many +directory levels have snuck into the core by running the following in the +top-level source directory: + + $ perl -ne "$_=~s/\s+.*//; print if scalar(split /\//) > 8;" < MANIFEST + The VMS::Filespec module, which gets installed as part of the build process on VMS, is a pure Perl module that can easily be installed on non-VMS platforms and can be helpful for conversions to and from RMS -native formats. +native formats. It is also now the only way that you should check to +see if VMS is in a case sensitive mode. What C<\n> represents depends on the type of file opened. It usually represents C<\012> but it could also be C<\015>, C<\012>, C<\015\012>, -C<\000>, C<\040>, or nothing depending on the file organiztion and +C<\000>, C<\040>, or nothing depending on the file organization and record format. The VMS::Stdio module provides access to the special fopen() requirements of files with unusual attributes on VMS. TCP/IP stacks are optional on VMS, so socket routines might not be implemented. UDP sockets may not be supported. +The TCP/IP library support for all current versions of VMS is dynamically +loaded if present, so even if the routines are configured, they may +return a status indicating that they are not implemented. + The value of C<$^O> on OpenVMS is "VMS". To determine the architecture that you are running on without resorting to loading all of C<%Config> you can examine the content of the C<@INC> array like so: @@ -1037,10 +1124,16 @@ you can examine the content of the C<@INC> array like so: } elsif (grep(/VMS_VAX/, @INC)) { print "I'm on VAX!\n"; + } elsif (grep(/VMS_IA64/, @INC)) { + print "I'm on IA64!\n"; + } else { print "I'm not so sure about where $^O is...\n"; } +In general, the significant differences should only be if Perl is running +on VMS_VAX or one of the 64 bit OpenVMS platforms. + On VMS, perl determines the UTC offset from the C logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00, calls to C are adjusted to count offsets from @@ -1052,50 +1145,63 @@ Also see: =item * -F (installed as L), L +F (installed as F), L =item * -vmsperl list, majordomo@perl.org - -(Put the words C in message body.) +vmsperl list, vmsperl-subscribe@perl.org =item * -vmsperl on the web, http://www.sidhe.org/vmsperl/index.html +vmsperl on the web, L =back =head2 VOS -Perl on VOS is discussed in F in the perl distribution -(installed as L). Perl on VOS can accept either VOS- or -Unix-style file specifications as in either of the following: +Perl on VOS (also known as OpenVOS) is discussed in F +in the perl distribution (installed as L). Perl on VOS +can accept either VOS- or Unix-style file specifications as in +either of the following: - C<< $ perl -ne "print if /perl_setup/i" >system>notices >> - C<< $ perl -ne "print if /perl_setup/i" /system/notices >> + $ perl -ne "print if /perl_setup/i" >system>notices + $ perl -ne "print if /perl_setup/i" /system/notices or even a mixture of both as in: - C<< $ perl -ne "print if /perl_setup/i" >system/notices >> + $ perl -ne "print if /perl_setup/i" >system/notices Even though VOS allows the slash character to appear in object names, because the VOS port of Perl interprets it as a pathname -delimiting character, VOS files, directories, or links whose names -contain a slash character cannot be processed. Such files must be -renamed before they can be processed by Perl. Note that VOS limits -file names to 32 or fewer characters. - -Perl on VOS can be built using two different compilers and two different -versions of the POSIX runtime. The recommended method for building full -Perl is with the GNU C compiler and the generally-available version of -VOS POSIX support. See F (installed as L) for -restrictions that apply when Perl is built using the VOS Standard C -compiler or the alpha version of VOS POSIX support. - -The value of C<$^O> on VOS is "VOS". To determine the architecture that -you are running on without resorting to loading all of C<%Config> you -can examine the content of the @INC array like so: +delimiting character, VOS files, directories, or links whose +names contain a slash character cannot be processed. Such files +must be renamed before they can be processed by Perl. + +Older releases of VOS (prior to OpenVOS Release 17.0) limit file +names to 32 or fewer characters, prohibit file names from +starting with a C<-> character, and prohibit file names from +containing any character matching C<< tr/ !#%&'()*;<=>?// >>. + +Newer releases of VOS (OpenVOS Release 17.0 or later) support a +feature known as extended names. On these releases, file names +can contain up to 255 characters, are prohibited from starting +with a C<-> character, and the set of prohibited characters is +reduced to any character matching C<< tr/#%*<>?// >>. There are +restrictions involving spaces and apostrophes: these characters +must not begin or end a name, nor can they immediately precede or +follow a period. Additionally, a space must not immediately +precede another space or hyphen. Specifically, the following +character combinations are prohibited: space-space, +space-hyphen, period-space, space-period, period-apostrophe, +apostrophe-period, leading or trailing space, and leading or +trailing apostrophe. Although an extended file name is limited +to 255 characters, a path name is still limited to 256 +characters. + +The value of C<$^O> on VOS is "VOS". To determine the +architecture that you are running on without resorting to loading +all of C<%Config> you can examine the content of the @INC array +like so: if ($^O =~ /VOS/) { print "I'm on a Stratus box!\n"; @@ -1104,19 +1210,6 @@ can examine the content of the @INC array like so: die; } - if (grep(/860/, @INC)) { - print "This box is a Stratus XA/R!\n"; - - } elsif (grep(/7100/, @INC)) { - print "This box is a Stratus HP 7100 or 8xxx!\n"; - - } elsif (grep(/8000/, @INC)) { - print "This box is a Stratus HP 8xxx!\n"; - - } else { - print "This box is a Stratus 68K!\n"; - } - Also see: =over 4 @@ -1130,13 +1223,13 @@ F (installed as L) The VOS mailing list. There is no specific mailing list for Perl on VOS. You can post -comments to the comp.sys.stratus newsgroup, or subscribe to the general -Stratus mailing list. Send a letter with "subscribe Info-Stratus" in -the message body to majordomo@list.stratagy.com. +comments to the comp.sys.stratus newsgroup, or use the contact +information located in the distribution files on the Stratus +Anonymous FTP site. =item * -VOS Perl on the web at http://ftp.stratus.com/pub/vos/posix/posix.html +VOS Perl on the web at L =back @@ -1149,7 +1242,9 @@ Character Code Set ID 0037 for OS/400 and either 1047 or POSIX-BC for S/390 systems). On the mainframe perl currently works under the "Unix system services for OS/390" (formerly known as OpenEdition), VM/ESA OpenEdition, or the BS200 POSIX-BC system (BS2000 is supported in perl 5.6 and greater). -See L for details. +See L for details. Note that for OS/400 there is also a port of +Perl 5.8.1/5.9.0 or later to the PASE which is ASCII-based (as opposed to +ILE which is EBCDIC-based), see L. As of R2.5 of USS for OS/390 and Version 2.3 of VM/ESA these Unix sub-systems do not support the C<#!> shebang trick for script invocation. @@ -1203,7 +1298,7 @@ The values of C<$^O> on some of these platforms includes: Some simple tricks for determining if you are running on an EBCDIC platform could include any of the following (perhaps all): - if ("\t" eq "\05") { print "EBCDIC may be spoken here!\n"; } + if ("\t" eq "\005") { print "EBCDIC may be spoken here!\n"; } if (ord('A') == 193) { print "EBCDIC may be spoken here!\n"; } @@ -1220,8 +1315,6 @@ Also see: =item * -* - L, F, F, F, L. @@ -1231,10 +1324,10 @@ The perl-mvs@perl.org list is for discussion of porting issues as well as general usage issues for all EBCDIC Perls. Send a message body of "subscribe perl-mvs" to majordomo@perl.org. -=item * +=item * AS/400 Perl information at -http://as400.rochester.ibm.com/ +L as well as on CPAN in the F directory. =back @@ -1301,8 +1394,8 @@ subdirectories named after the suffix. Hence files are translated: The Unix emulation library's translation of filenames to native assumes that this sort of translation is required, and it allows a user-defined list of known suffixes that it will transpose in this fashion. This may -seem transparent, but consider that with these rules C -and C both map to C, and that C and +seem transparent, but consider that with these rules F +and F both map to F, and that C and C cannot and do not attempt to emulate the reverse mapping. Other C<.>'s in filenames are translated to C. @@ -1345,13 +1438,13 @@ in C<$^O> is "riscos" (because we don't like shouting). =head2 Other perls Perl has been ported to many platforms that do not fit into any of -the categories listed above. Some, such as AmigaOS, Atari MiNT, -BeOS, HP MPE/iX, QNX, Plan 9, and VOS, have been well-integrated -into the standard Perl source code kit. You may need to see the -F directory on CPAN for information, and possibly binaries, -for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware, -Tandem Guardian, I (Yes, we know that some of these OSes may -fall under the Unix category, but we are not a standards body.) +the categories listed above. Some, such as AmigaOS, BeOS, HP MPE/iX, +QNX, Plan 9, and VOS, have been well-integrated into the standard +Perl source code kit. You may need to see the F directory +on CPAN for information, and possibly binaries, for the likes of: +aos, Atari ST, lynxos, riscos, Novell Netware, Tandem Guardian, +I (Yes, we know that some of these OSes may fall under the +Unix category, but we are not a standards body.) Some approximate operating system names and their C<$^O> values in the "OTHER" category include: @@ -1372,27 +1465,22 @@ Amiga, F (installed as L). =item * -Atari, F and Guido Flohr's web page -http://stud.uni-sb.de/~gufl0000/ - -=item * - Be OS, F =item * HP 300 MPE/iX, F and Mark Bixby's web page -http://www.bixby.org/mark/perlix.html +L =item * A free perl5-based PERL.NLM for Novell Netware is available in -precompiled binary and source code form from http://www.novell.com/ +precompiled binary and source code form from L as well as from CPAN. =item * -Plan 9, F +S, F =back @@ -1419,57 +1507,57 @@ L for a full description of available variables. =over 8 -=item -X FILEHANDLE - -=item -X EXPR - =item -X -C<-r>, C<-w>, and C<-x> have a limited meaning only; directories -and applications are executable, and there are no uid/gid -considerations. C<-o> is not supported. (S) +C<-w> only inspects the read-only file attribute (FILE_ATTRIBUTE_READONLY), +which determines whether the directory can be deleted, not whether it can +be written to. Directories always have read and write access unless denied +by discretionary access control lists (DACLs). (S) C<-r>, C<-w>, C<-x>, and C<-o> tell whether the file is accessible, which may not reflect UIC-based file protections. (VMS) -C<-s> returns the size of the data fork, not the total size of data fork -plus resource fork. (S). - C<-s> by name on an open file will return the space reserved on disk, rather than the current extent. C<-s> on an open filehandle returns the current size. (S) C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>, -C<-x>, C<-o>. (S, Win32, VMS, S) +C<-x>, C<-o>. (Win32, VMS, S) -C<-b>, C<-c>, C<-k>, C<-g>, C<-p>, C<-u>, C<-A> are not implemented. -(S) - -C<-g>, C<-k>, C<-l>, C<-p>, C<-u>, C<-A> are not particularly meaningful. +C<-g>, C<-k>, C<-l>, C<-u>, C<-A> are not particularly meaningful. (Win32, VMS, S) +C<-p> is not particularly meaningful. (VMS, S) + C<-d> is true if passed a device spec without an explicit directory. (VMS) -C<-T> and C<-B> are implemented, but might misclassify Mac text files -with foreign characters; this is the case will all platforms, but may -affect S often. (S) - C<-x> (or C<-X>) determine if a file ends in one of the executable suffixes. C<-S> is meaningless. (Win32) C<-x> (or C<-X>) determine if a file has an executable file type. (S) -=item alarm SECONDS - =item alarm -Not implemented. (Win32) +Emulated using timers that must be explicitly polled whenever Perl +wants to dispatch "safe signals" and therefore cannot interrupt +blocking system calls. (Win32) + +=item atan2 -=item binmode FILEHANDLE +Due to issues with various CPUs, math libraries, compilers, and standards, +results for C may vary depending on any combination of the above. +Perl attempts to conform to the Open Group/IEEE standards for the results +returned from C, but cannot force the issue if the system Perl is +run on does not allow it. (Tru64, HP-UX 10.20) -Meaningless. (S, S) +The current version of the standards for C is available at +L. + +=item binmode + +Meaningless. (S) Reopens file and restores pointer; if function fails, underlying filehandle may be closed, or pointer may be in a different position. @@ -1478,10 +1566,7 @@ filehandle may be closed, or pointer may be in a different position. The value returned by C may be affected after the call, and the filehandle may be flushed. (Win32) -=item chmod LIST - -Only limited meaning. Disabling/enabling write permission is mapped to -locking/unlocking the file. (S) +=item chmod Only good for changing "owner" read-write access, "group", and "other" bits are meaningless. (Win32) @@ -1493,74 +1578,82 @@ Access permissions are mapped onto VOS access-control list changes. (VOS) The actual permissions set depend on the value of the C in the SYSTEM environment settings. (Cygwin) -=item chown LIST +=item chown -Not implemented. (S, Win32, Plan9, S, VOS) +Not implemented. (Win32, S, S) Does nothing, but won't fail. (Win32) -=item chroot FILENAME +A little funky, because VOS's notion of ownership is a little funky (VOS). =item chroot -Not implemented. (S, Win32, VMS, Plan9, S, VOS, VM/ESA) +Not implemented. (Win32, VMS, S, S, VOS, VM/ESA) -=item crypt PLAINTEXT,SALT +=item crypt May not be available if library or source was not provided when building perl. (Win32) -Not implemented. (VOS) +=item dbmclose -=item dbmclose HASH +Not implemented. (VMS, S, VOS) -Not implemented. (VMS, Plan9, VOS) +=item dbmopen -=item dbmopen HASH,DBNAME,MODE +Not implemented. (VMS, S, VOS) -Not implemented. (VMS, Plan9, VOS) +=item dump -=item dump LABEL - -Not useful. (S, S) +Not useful. (S) -Not implemented. (Win32) +Not supported. (Cygwin, Win32) Invokes VMS debugger. (VMS) -=item exec LIST - -Not implemented. (S) +=item exec Implemented via Spawn. (VM/ESA) Does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX) -=item exit EXPR +Not supported. (Symbian OS) =item exit -Emulates UNIX exit() (which considers C to indicate an error) by +Emulates Unix exit() (which considers C to indicate an error) by mapping the C<1> to SS$_ABORT (C<44>). This behavior may be overridden with the pragma C. As with the CRTL's exit() function, C is also mapped to an exit status of SS$_NORMAL (C<1>); this mapping cannot be overridden. Any other argument to exit() -is used directly as Perl's exit status. (VMS) +is used directly as Perl's exit status. On VMS, unless the future +POSIX_EXIT mode is enabled, the exit code should always be a valid +VMS exit code and not a generic number. When the POSIX_EXIT mode is +enabled, a generic number will be encoded in a method compatible with +the C library _POSIX_EXIT macro so that it can be decoded by other +programs, particularly ones written in C, like the GNV package. (VMS) + +C resets file pointers, which is a problem when called +from a child process (created by C) in C. +A workaround is to use C. (Solaris) + + exit unless $Config{archname} =~ /\bsolaris\b/; + require POSIX and POSIX::_exit(0); -=item fcntl FILEHANDLE,FUNCTION,SCALAR +=item fcntl -Not implemented. (Win32, VMS) +Not implemented. (Win32) -=item flock FILEHANDLE,OPERATION +Some functions available based on the version of VMS. (VMS) -Not implemented (S, VMS, S, VOS). +=item flock -Available only on Windows NT (not on Windows 95). (Win32) +Not implemented (VMS, S, VOS). =item fork -Not implemented. (S, AmigaOS, S, VOS, VM/ESA) +Not implemented. (AmigaOS, S, VM/ESA, VMS) Emulated using multiple interpreters. See L. (Win32) @@ -1569,131 +1662,139 @@ Does not automatically flush output handles on some platforms. =item getlogin -Not implemented. (S, S) +Not implemented. (S) -=item getpgrp PID +=item getpgrp -Not implemented. (S, Win32, VMS, S, VOS) +Not implemented. (Win32, VMS, S) =item getppid -Not implemented. (S, Win32, VMS, S) +Not implemented. (Win32, S) -=item getpriority WHICH,WHO +=item getpriority -Not implemented. (S, Win32, VMS, S, VOS, VM/ESA) +Not implemented. (Win32, VMS, S, VOS, VM/ESA) -=item getpwnam NAME +=item getpwnam -Not implemented. (S, Win32) +Not implemented. (Win32) Not useful. (S) -=item getgrnam NAME +=item getgrnam -Not implemented. (S, Win32, VMS, S) +Not implemented. (Win32, VMS, S) -=item getnetbyname NAME +=item getnetbyname -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, S) -=item getpwuid UID +=item getpwuid -Not implemented. (S, Win32) +Not implemented. (Win32) Not useful. (S) -=item getgrgid GID +=item getgrgid -Not implemented. (S, Win32, VMS, S) - -=item getnetbyaddr ADDR,ADDRTYPE - -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, VMS, S) -=item getprotobynumber NUMBER +=item getnetbyaddr -Not implemented. (S) +Not implemented. (Win32, S) -=item getservbyport PORT,PROTO +=item getprotobynumber -Not implemented. (S) +=item getservbyport =item getpwent -Not implemented. (S, Win32, VM/ESA) +Not implemented. (Win32, VM/ESA) =item getgrent -Not implemented. (S, Win32, VMS, VM/ESA) +Not implemented. (Win32, VMS, VM/ESA) + +=item gethostbyname + +C does not work everywhere: you may have +to use C. (S) =item gethostent -Not implemented. (S, Win32) +Not implemented. (Win32) =item getnetent -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, S) =item getprotoent -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, S) =item getservent -Not implemented. (Win32, Plan9) +Not implemented. (Win32, S) -=item sethostent STAYOPEN +=item sethostent -Not implemented. (S, Win32, Plan9, S) +Not implemented. (Win32, S, S) -=item setnetent STAYOPEN +=item setnetent -Not implemented. (S, Win32, Plan9, S) +Not implemented. (Win32, S, S) -=item setprotoent STAYOPEN +=item setprotoent -Not implemented. (S, Win32, Plan9, S) +Not implemented. (Win32, S, S) -=item setservent STAYOPEN +=item setservent -Not implemented. (Plan9, Win32, S) +Not implemented. (S, Win32, S) =item endpwent -Not implemented. (S, MPE/iX, VM/ESA, Win32) +Not implemented. (MPE/iX, VM/ESA, Win32) =item endgrent -Not implemented. (S, MPE/iX, S, VM/ESA, VMS, Win32) +Not implemented. (MPE/iX, S, VM/ESA, VMS, Win32) =item endhostent -Not implemented. (S, Win32) +Not implemented. (Win32) =item endnetent -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, S) =item endprotoent -Not implemented. (S, Win32, Plan9) +Not implemented. (Win32, S) =item endservent -Not implemented. (Plan9, Win32) +Not implemented. (S, Win32) =item getsockopt SOCKET,LEVEL,OPTNAME -Not implemented. (Plan9) - -=item glob EXPR +Not implemented. (S) =item glob This operator is implemented via the File::Glob extension on most platforms. See L for portability information. +=item gmtime + +In theory, gmtime() is reliable from -2**63 to 2**63-1. However, +because work arounds in the implementation use floating point numbers, +it will become inaccurate as the time gets larger. This is a bug and +will be fixed in the future. + +On VOS, time values are 32-bit quantities. + =item ioctl FILEHANDLE,FUNCTION,SCALAR Not implemented. (VMS) @@ -1703,10 +1804,7 @@ in the Winsock API does. (Win32) Available only for socket handles. (S) -=item kill SIGNAL, LIST - -C is implemented for the sake of taint checking; -use with other signals is unimplemented. (S) +=item kill Not implemented, hence not useful for taint checking. (S) @@ -1717,59 +1815,74 @@ and makes it exit immediately with exit status $sig. As in Unix, if $sig is 0 and the specified process exists, it returns true without actually terminating it. (Win32) -=item link OLDFILE,NEWFILE +C will terminate the process specified by $pid and +recursively all child processes owned by it. This is different from +the Unix semantics, where the signal will be delivered to all +processes in the same process group as the process specified by +$pid. (Win32) -Not implemented. (S, MPE/iX, VMS, S) +Is not supported for process identification number of 0 or negative +numbers. (VMS) + +=item link + +Not implemented. (MPE/iX, S, VOS) Link count not updated because hard links are not quite that hard (They are sort of half-way between hard and soft links). (AmigaOS) -Hard links are implemented on Win32 (Windows NT and Windows 2000) -under NTFS only. +Hard links are implemented on Win32 under NTFS only. They are +natively supported on Windows 2000 and later. On Windows NT they +are implemented using the Windows POSIX subsystem support and the +Perl process will need Administrator or Backup Operator privileges +to create hard links. + +Available on 64 bit OpenVMS 8.2 and later. (VMS) -=item lstat FILEHANDLE +=item localtime -=item lstat EXPR +localtime() has the same range as L, but because time zone +rules change its accuracy for historical and future times may degrade +but usually by no more than an hour. =item lstat -Not implemented. (VMS, S) +Not implemented. (S) Return values (especially for device and inode) may be bogus. (Win32) -=item msgctl ID,CMD,ARG +=item msgctl -=item msgget KEY,FLAGS +=item msgget -=item msgsnd ID,MSG,FLAGS +=item msgsnd -=item msgrcv ID,VAR,SIZE,TYPE,FLAGS +=item msgrcv -Not implemented. (S, Win32, VMS, Plan9, S, VOS) +Not implemented. (Win32, VMS, S, S, VOS) -=item open FILEHANDLE,EXPR +=item open -=item open FILEHANDLE - -The C<|> variants are supported only if ToolServer is installed. -(S) - -open to C<|-> and C<-|> are unsupported. (S, Win32, S) +open to C<|-> and C<-|> are unsupported. (Win32, S) Opening a process does not automatically flush output handles on some platforms. (SunOS, Solaris, HP-UX) -=item pipe READHANDLE,WRITEHANDLE +=item readlink + +Not implemented. (Win32, VMS, S) -Very limited functionality. (MiNT) +=item rename -=item readlink EXPR +Can't move directories between directories on different logical volumes. (Win32) -=item readlink +=item rewinddir -Not implemented. (Win32, VMS, S) +Will not cause readdir() to re-read the directory stream. The entries +already read before the rewinddir() call will just be returned again +from a cache buffer. (Win32) -=item select RBITS,WBITS,EBITS,TIMEOUT +=item select Only implemented on sockets. (Win32, VMS) @@ -1777,56 +1890,56 @@ Only reliable on sockets. (S) Note that the C