perlport.1

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

\&    for (my $x = 0; $x <= 10000000; ++$x) {}   # good
\&
\&    @lines = <VERY_LARGE_FILE>;                # bad
\&
\&    while (<FILE>) {$file .= $_}               # sometimes bad
\&    $file = join(\*(Aq\*(Aq, <FILE>);                  # better
.Ve
.PP
The last two constructs may appear unintuitive to most people.  The
first repeatedly grows a string, whereas the second allocates a
large chunk of memory in one go.  On some systems, the second is
more efficient that the first.
.Sh "Security"
.IX Subsection "Security"
Most multi-user platforms provide basic levels of security, usually
implemented at the filesystem level.  Some, however, do
not\*(-- unfortunately.  Thus the notion of user id, or \*(L"home\*(R" directory,
or even the state of being logged-in, may be unrecognizable on many
platforms.  If you write programs that are security-conscious, it
is usually best to know what type of system you will be running
under so that you can write code explicitly for that platform (or
class of platforms).
.PP
Don't assume the \s-1UNIX\s0 filesystem access semantics: the operating
system or the filesystem may be using some \s-1ACL\s0 systems, which are
richer languages than the usual rwx.  Even if the rwx exist,
their semantics might be different.
.PP
(From security viewpoint testing for permissions before attempting to
do something is silly anyway: if one tries this, there is potential
for race conditions\*(-- someone or something might change the
permissions between the permissions check and the actual operation.
Just try the operation.)
.PP
Don't assume the \s-1UNIX\s0 user and group semantics: especially, don't
expect the \f(CW$<\fR and \f(CW$>\fR (or the \f(CW$(\fR and \f(CW$)\fR) to work
for switching identities (or memberships).
.PP
Don't assume set-uid and set-gid semantics. (And even if you do,
think twice: set-uid and set-gid are a known can of security worms.)
.Sh "Style"
.IX Subsection "Style"
For those times when it is necessary to have platform-specific code,
consider keeping the platform-specific code in one place, making porting
to other platforms easier.  Use the Config module and the special
variable \f(CW$^O\fR to differentiate platforms, as described in
\&\*(L"\s-1PLATFORMS\s0\*(R".
.PP
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
\&\f(CW$!\fR after a failed system call.  Using \f(CW$!\fR 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.
.SH "CPAN Testers"
.IX Header "CPAN Testers"
Modules uploaded to \s-1CPAN\s0 are tested by a variety of volunteers on
different platforms.  These \s-1CPAN\s0 testers are notified by mail of each
new upload, and reply to the list with \s-1PASS\s0, \s-1FAIL\s0, \s-1NA\s0 (not applicable to
this platform), or \s-1UNKNOWN\s0 (unknown), along with any relevant notations.
.PP
The purpose of the testing is twofold: one, to help developers fix any
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.
.PP
Also see:
.IP "\(bu" 4
Mailing list: cpan\[e-mail]
.IP "\(bu" 4
Testing results: http://testers.cpan.org/
.SH "PLATFORMS"
.IX Header "PLATFORMS"
As of version 5.002, Perl is built with a \f(CW$^O\fR variable that
indicates the operating system it was built on.  This was implemented
to help speed up code that would otherwise have to \f(CW\*(C`use Config\*(C'\fR
and use the value of \f(CW$Config{osname}\fR.  Of course, to get more
detailed information about the system, looking into \f(CW%Config\fR is
certainly recommended.
.PP
\&\f(CW%Config\fR cannot always be trusted, however, because it was built
at compile time.  If perl was built in one place, then transferred
elsewhere, some values may be wrong.  The values may even have been
edited after the fact.
.Sh "Unix"
.IX Subsection "Unix"
Perl works on a bewildering variety of Unix and Unix-like platforms (see
e.g. most of the files in the \fIhints/\fR directory in the source code kit).
On most of these systems, the value of \f(CW$^O\fR (hence \f(CW$Config{\*(Aqosname\*(Aq}\fR,
too) is determined either by lowercasing and stripping punctuation from the
first field of the string returned by typing \f(CW\*(C`uname \-a\*(C'\fR (or a similar command)
at the shell prompt or by testing the file system for the presence of
uniquely named files such as a kernel or header file.  Here, for example,
are a few of the more popular Unix flavors:
.PP
.Vb 10
\&    uname         $^O        $Config{\*(Aqarchname\*(Aq}
\&    \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\&    AIX           aix        aix
\&    BSD/OS        bsdos      i386\-bsdos
\&    Darwin        darwin     darwin
\&    dgux          dgux       AViiON\-dgux
\&    DYNIX/ptx     dynixptx   i386\-dynixptx
\&    FreeBSD       freebsd    freebsd\-i386    
\&    Linux         linux      arm\-linux
\&    Linux         linux      i386\-linux
\&    Linux         linux      i586\-linux
\&    Linux         linux      ppc\-linux
\&    HP\-UX         hpux       PA\-RISC1.1
\&    IRIX          irix       irix
\&    Mac OS X      darwin     darwin
\&    MachTen PPC   machten    powerpc\-machten
\&    NeXT 3        next       next\-fat
\&    NeXT 4        next       OPENSTEP\-Mach
\&    openbsd       openbsd    i386\-openbsd
\&    OSF1          dec_osf    alpha\-dec_osf
\&    reliantunix\-n svr4       RM400\-svr4
\&    SCO_SV        sco_sv     i386\-sco_sv
\&    SINIX\-N       svr4       RM400\-svr4
\&    sn4609        unicos     CRAY_C90\-unicos
\&    sn6521        unicosmk   t3e\-unicosmk
\&    sn9617        unicos     CRAY_J90\-unicos
\&    SunOS         solaris    sun4\-solaris
\&    SunOS         solaris    i86pc\-solaris
\&    SunOS4        sunos      sun4\-sunos
.Ve
.PP
Because the value of \f(CW$Config{archname}\fR may depend on the
hardware architecture, it can vary more than the value of \f(CW$^O\fR.
.Sh "\s-1DOS\s0 and Derivatives"
.IX Subsection "DOS and Derivatives"
Perl has long been ported to Intel-style microcomputers running under
systems like PC-DOS, MS-DOS, \s-1OS/2\s0, and most Windows platforms you can
bring yourself to mention (except for Windows \s-1CE\s0, if you count that).
Users familiar with \fI\s-1COMMAND\s0.COM\fR or \fI\s-1CMD\s0.EXE\fR style shells should
be aware that each of these file specifications may have subtle
differences:
.PP
.Vb 4
\&    $filespec0 = "c:/foo/bar/file.txt";
\&    $filespec1 = "c:\e\efoo\e\ebar\e\efile.txt";
\&    $filespec2 = \*(Aqc:\efoo\ebar\efile.txt\*(Aq;
\&    $filespec3 = \*(Aqc:\e\efoo\e\ebar\e\efile.txt\*(Aq;
.Ve
.PP
System calls accept either \f(CW\*(C`/\*(C'\fR or \f(CW\*(C`\e\*(C'\fR as the path separator.
However, many command-line utilities of \s-1DOS\s0 vintage treat \f(CW\*(C`/\*(C'\fR as
the option prefix, so may get confused by filenames containing \f(CW\*(C`/\*(C'\fR.
Aside from calling any external programs, \f(CW\*(C`/\*(C'\fR will work just fine,
and probably better, as it is more consistent with popular usage,
and avoids the problem of remembering what to backwhack and what
not to.
.PP
The \s-1DOS\s0 \s-1FAT\s0 filesystem can accommodate only \*(L"8.3\*(R" style filenames.  Under
the \*(L"case-insensitive, but case-preserving\*(R" \s-1HPFS\s0 (\s-1OS/2\s0) and \s-1NTFS\s0 (\s-1NT\s0)
filesystems you may have to be careful about case returned with functions
like \f(CW\*(C`readdir\*(C'\fR or used with functions like \f(CW\*(C`open\*(C'\fR or \f(CW\*(C`opendir\*(C'\fR.
.PP
\&\s-1DOS\s0 also treats several filenames as special, such as \s-1AUX\s0, \s-1PRN\s0,
\&\s-1NUL\s0, \s-1CON\s0, \s-1COM1\s0, \s-1LPT1\s0, \s-1LPT2\s0, etc.  Unfortunately, sometimes these
filenames won't even work if you include an explicit directory
prefix.  It is best to avoid such filenames, if you want your code
to be portable to \s-1DOS\s0 and its derivatives.  It's hard to know what
these all are, unfortunately.
.PP
Users of these operating systems may also wish to make use of
scripts such as \fIpl2bat.bat\fR or \fIpl2cmd\fR to
put wrappers around your scripts.
.PP
Newline (\f(CW\*(C`\en\*(C'\fR) is translated as \f(CW\*(C`\e015\e012\*(C'\fR by \s-1STDIO\s0 when reading from
and writing to files (see \*(L"Newlines\*(R").  \f(CW\*(C`binmode(FILEHANDLE)\*(C'\fR
will keep \f(CW\*(C`\en\*(C'\fR translated as \f(CW\*(C`\e012\*(C'\fR for that filehandle.  Since it is a
no-op on other systems, \f(CW\*(C`binmode\*(C'\fR should be used for cross-platform code
that deals with binary data.  That's assuming you realize in advance
that your data is in binary.  General-purpose programs should
often assume nothing about their data.
.PP
The \f(CW$^O\fR variable and the \f(CW$Config{archname}\fR values for various
DOSish perls are as follows:
.PP
.Vb 10
\&     OS            $^O      $Config{archname}   ID    Version
\&     \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-
\&     MS\-DOS        dos        ?                 
\&     PC\-DOS        dos        ?                 
\&     OS/2          os2        ?
\&     Windows 3.1   ?          ?                 0      3 01
\&     Windows 95    MSWin32    MSWin32\-x86       1      4 00
\&     Windows 98    MSWin32    MSWin32\-x86       1      4 10
\&     Windows ME    MSWin32    MSWin32\-x86       1      ?
\&     Windows NT    MSWin32    MSWin32\-x86       2      4 xx
\&     Windows NT    MSWin32    MSWin32\-ALPHA     2      4 xx
\&     Windows NT    MSWin32    MSWin32\-ppc       2      4 xx
\&     Windows 2000  MSWin32    MSWin32\-x86       2      5 00
\&     Windows XP    MSWin32    MSWin32\-x86       2      5 01
\&     Windows 2003  MSWin32    MSWin32\-x86       2      5 02
\&     Windows CE    MSWin32    ?                 3           
\&     Cygwin        cygwin     cygwin
.Ve
.PP
The various MSWin32 Perl's can distinguish the \s-1OS\s0 they are running on
via the value of the fifth element of the list returned from 
\&\fIWin32::GetOSVersion()\fR.  For example:
.PP
.Vb 4
\&    if ($^O eq \*(AqMSWin32\*(Aq) {
\&        my @os_version_info = Win32::GetOSVersion();
\&        print +(\*(Aq3.1\*(Aq,\*(Aq95\*(Aq,\*(AqNT\*(Aq)[$os_version_info[4]],"\en";
\&    }
.Ve
.PP
There are also \fIWin32::IsWinNT()\fR and \fIWin32::IsWin95()\fR, try \f(CW\*(C`perldoc Win32\*(C'\fR,
and as of libwin32 0.19 (not part of the core Perl distribution)
\&\fIWin32::GetOSName()\fR.  The very portable \fIPOSIX::uname()\fR will work too:
.PP
.Vb 2
\&    c:\e> perl \-MPOSIX \-we "print join \*(Aq|\*(Aq, uname"
\&    Windows NT|moonru|5.0|Build 2195 (Service Pack 2)|x86
.Ve
.PP
Also see:
.IP "\(bu" 4
The djgpp environment for \s-1DOS\s0, http://www.delorie.com/djgpp/
and perldos.
.IP "\(bu" 4
The \s-1EMX\s0 environment for \s-1DOS\s0, \s-1OS/2\s0, etc. [e-mail],
http://www.leo.org/pub/comp/os/os2/leo/gnu/emx+gcc/index.html or
ftp://hobbes.nmsu.edu/pub/os2/dev/emx/  Also perlos2.
.IP "\(bu" 4
Build instructions for Win32 in perlwin32, or under the Cygnus environment
in perlcygwin.
.IP "\(bu" 4
The \f(CW\*(C`Win32::*\*(C'\fR modules in Win32.
.IP "\(bu" 4
The ActiveState Pages, http://www.activestate.com/
.IP "\(bu" 4
The Cygwin environment for Win32; \fI\s-1README\s0.cygwin\fR (installed 
as perlcygwin), http://www.cygwin.com/
.IP "\(bu" 4
The U/WIN environment for Win32,
http://www.research.att.com/sw/tools/uwin/
.IP "\(bu" 4
Build instructions for \s-1OS/2\s0, perlos2
.Sh "Mac\ \s-1OS\s0"
.IX Subsection "MacOS"
Any module requiring \s-1XS\s0 compilation is right out for most people, because
MacPerl is built using non-free (and non-cheap!) compilers.  Some \s-1XS\s0
modules that can work with MacPerl are built and distributed in binary
form on \s-1CPAN\s0.
.PP
Directories are specified as:
.PP
.Vb 6
\&    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
.Ve
.PP
Files are stored in the directory in alphabetical order.  Filenames are
limited to 31 characters, and may include any character except for
null and \f(CW\*(C`:\*(C'\fR, which is reserved as the path separator.
.PP
Instead of \f(CW\*(C`flock\*(C'\fR, see \f(CW\*(C`FSpSetFLock\*(C'\fR and \f(CW\*(C`FSpRstFLock\*(C'\fR in the
Mac::Files module, or \f(CW\*(C`chmod(0444, ...)\*(C'\fR and \f(CW\*(C`chmod(0666, ...)\*(C'\fR.
.PP
In the MacPerl application, you can't run a program from the command line;
programs that expect \f(CW@ARGV\fR to be populated can be edited with something
like the following, which brings up a dialog box asking for the command
line arguments.
.PP
.Vb 3
\&    if (!@ARGV) {
\&        @ARGV = split /\es+/, MacPerl::Ask(\*(AqArguments?\*(Aq);
\&    }