perlport - Writing portable Perl
-
=head1 DESCRIPTION
-Perl runs on a variety of operating systems. While most of them share
-a lot in common, they also have their own very particular and unique
-features.
+Perl runs on numerous operating systems. While most of them share
+much in common, they also have their own unique features.
This document is meant to help you to find out what constitutes portable
-Perl code, so that once you have made your decision to write portably,
+Perl code. That way once you make a decision to write portably,
you know where the lines are drawn, and you can stay within them.
-There is a tradeoff between taking full advantage of one particular type
-of computer, and taking advantage of a full range of them. Naturally,
-as you make your range bigger (and thus more diverse), the common
-denominators drop, and you are left with fewer areas of common ground in
-which you can operate to accomplish a particular task. Thus, when you
-begin attacking a problem, it is important to consider which part of the
-tradeoff curve you want to operate under. Specifically, whether it is
-important to you that the task that you are coding needs the full
-generality of being portable, or if it is sufficient to just get the job
-done. This is the hardest choice to be made. The rest is easy, because
-Perl provides lots of choices, whichever way you want to approach your
+There is a tradeoff between taking full advantage of one particular
+type of computer and taking advantage of a full range of them.
+Naturally, as you broaden your range and become more diverse, the
+common factors drop, and you are left with an increasingly smaller
+area of common ground in which you can operate to accomplish a
+particular task. Thus, when you begin attacking a problem, it is
+important to consider under which part of the tradeoff curve you
+want to operate. Specifically, you must decide whether it is
+important that the task that you are coding have the full generality
+of being portable, or whether to just get the job done right now.
+This is the hardest choice to be made. The rest is easy, because
+Perl provides many choices, whichever way you want to approach your
problem.
Looking at it another way, writing portable code is usually about
-willfully limiting your available choices. Naturally, it takes discipline
-to do that.
+willfully limiting your available choices. Naturally, it takes
+discipline and sacrifice to do that. The product of portability
+and convenience may be a constant. You have been warned.
Be aware of two important points:
-
=over 4
=item Not all Perl programs have to be portable
-There is no reason why you should not use Perl as a language to glue Unix
+There is no reason you should not use Perl as a language to glue Unix
tools together, or to prototype a Macintosh application, or to manage the
Windows registry. If it makes no sense to aim for portability for one
reason or another in a given program, then don't bother.
-=item The vast majority of Perl I<is> portable
+=item Nearly all of Perl already I<is> portable
Don't be fooled into thinking that it is hard to create portable Perl
code. It isn't. Perl tries its level-best to bridge the gaps between
=back
-
-Here's the general rule: When you approach a task that is commonly done
-using a whole range of platforms, think in terms of writing portable
+Here's the general rule: When you approach a task commonly done
+using a whole range of platforms, think about writing portable
code. That way, you don't sacrifice much by way of the implementation
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
often the case with systems programming (whether for Unix, Windows,
S<Mac OS>, VMS, etc.), consider writing platform-specific code.
-When the code will run on only two or three operating systems, then you
-may only need to consider the differences of those particular systems.
-The important thing is to decide where the code will run, and to be
+When the code will run on only two or three operating systems, you
+may need to consider only the differences of those particular systems.
+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
-builtin perl functions that behave differently on various ports
+built-in perl functions that behave differently on various ports
(L<"FUNCTION IMPLEMENTATIONS">.
This information should not be considered complete; it includes possibly
transient information about idiosyncrasies of some of the ports, almost
-all of which are in a state of constant evolution. Thus this material
+all of which are in a state of constant evolution. Thus, this material
should be considered a perpetual work in progress
(E<lt>IMG SRC="yellow_sign.gif" ALT="Under Construction"E<gt>).
-
=head1 ISSUES
=head2 Newlines
In most operating systems, lines in files are terminated by newlines.
Just what is used as a newline may vary from OS to OS. Unix
-traditionally uses C<\012>, one kind of Windows I/O uses C<\015\012>,
+traditionally uses C<\012>, one type of DOSish I/O uses C<\015\012>,
and S<Mac OS> 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>. C<\015\012> is commonly referred to as CRLF.
-
-Due to the "text" mode translation, DOSish perls have limitations
-of using C<seek> and C<tell> when a file is being accessed in "text"
-mode. Specifically, if you stick to C<seek>-ing to locations you got
-from C<tell> (and no others), you are usually free to use C<seek> and
-C<tell> even in "text" mode. In general, using C<seek> or C<tell> or
-other file operations that count bytes instead of characters, without
-considering the length of C<\n>, may be non-portable. If you use
-C<binmode> on a file, however, you can usually use C<seek> and C<tell>
-with arbitrary values quite safely.
+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 your reading or writing.
+Unix does the same thing on ttys in canonical mode. C<\015\012>
+is commonly referred to as CRLF.
+
+Because of the "text" mode translation, DOSish perls have limitations
+in using C<seek> and C<tell> on a file accessed in "text" mode.
+Stick to C<seek>-ing to locations you got from C<tell> (and no
+others), and you are usually free to use C<seek> and C<tell> even
+in "text" mode. Using C<seek> or C<tell> or other file operations
+may be non-portable. If you use C<binmode> on a file, however, you
+can usually C<seek> and C<tell> with arbitrary values in safety.
A common misconception in socket programming is that C<\n> eq C<\012>
everywhere. When using protocols such as common Internet protocols,
print SOCKET "Hi there, client!$CRLF" # RIGHT
When reading from a socket, remember that the default input record
-separator C<$/> is C<\n>, but code like this should recognize C<$/> as
-C<\012> or C<\015\012>:
+separator C<$/> is C<\n>, but robust socket code will recognize as
+either C<\012> or C<\015\012> as end of line:
while (<SOCKET>) {
# ...
}
-Since both CRLF and LF end in LF, the input record separator can
-be set to LF, and the CR can be stripped later, if present. Better:
+Because both CRLF and LF end in LF, the input record separator can
+be set to LF and any CR stripped later. Better to write:
use Socket qw(:DEFAULT :crlf);
local($/) = LF; # not needed if $/ is already \012
# s/\015?\012/\n/; # same thing
}
-And this example is actually better than the previous one even for Unix
-platforms, because now any C<\015>'s (C<\cM>'s) are stripped out
+This example is preferred over the previous one--even for Unix
+platforms--because now any C<\015>'s (C<\cM>'s) are stripped out
(and there was much rejoicing).
Similarly, functions that return text data--such as a function that
-fetches a web page--should, in some cases, translate newlines before
-returning the data, if they've not yet been trsnalted to the local
-newline. Often one line of code will suffice:
+fetches a web page--should sometimes translate newlines before
+returning the data, if they've not yet been translated to the local
+newline representation. A single line of code will often suffice:
- $data =~ s/\015?\012/\n/g;
- return $data;
+ $data =~ s/\015?\012/\n/g;
+ return $data;
Some of this may be confusing. Here's a handy reference to the ASCII CR
and LF characters. You can print it out and stick it in your wallet.
---------------------------
* text-mode STDIO
+The Unix column assumes that you are not accessing a serial line
+(like a tty) in canonical mode. If you are, then CR on input becomes
+"\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.
-
=head2 Numbers endianness and Width
Different CPUs store integers and floating point numbers in different
orders (called I<endianness>) and widths (32-bit and 64-bit being the
-most common). This affects your programs if they attempt to transfer
-numbers in binary format from one CPU architecture to another over some
-channel, usually either "live" via network connection, or by storing the
-numbers to secondary storage such as a disk file.
+most common today). This affects your programs when they attempt to transfer
+numbers in binary format from one CPU architecture to another,
+usually either "live" via network connection, or by storing the
+numbers to secondary storage such as a disk file or tape.
-Conflicting storage orders make utter mess out of the numbers: if a
+Conflicting storage orders make utter mess out of the numbers. If a
little-endian host (Intel, Alpha) stores 0x12345678 (305419896 in
decimal), a big-endian host (Motorola, MIPS, Sparc, PA) reads it as
0x78563412 (2018915346 in decimal). To avoid this problem in network
(socket) connections use the C<pack> and C<unpack> formats C<n>
-and C<N>, the "network" orders. They are guaranteed to be portable.
+and C<N>, the "network" orders. These are guaranteed to be portable.
-Different widths can cause truncation even between platforms of equal
-endianness: the platform of shorter width loses the upper parts of the
+Differing widths can cause truncation even between platforms of equal
+endianness. The platform of shorter width loses the upper parts of the
number. There is no good solution for this problem except to avoid
transferring or storing raw binary numbers.
-One can circumnavigate both these problems in two ways: either
+One can circumnavigate both these problems in two ways. Either
transfer and store numbers always in text format, instead of raw
-binary, or consider using modules like Data::Dumper (included in
-the standard distribution as of Perl 5.005) and Storable.
-
-Also, don't depend on specific values returned from C<printf> and
-C<sprintf>. These in some cases may differ from platform to platform.
+binary, or else consider using modules like Data::Dumper (included in
+the standard distribution as of Perl 5.005) and Storable. Keeping
+all data as text significantly simplifies matters.
=head2 Files and Filesystems
Most platforms these days structure files in a hierarchical fashion.
-So, it is reasonably safe to assume that any platform supports the
+So, it is reasonably safe to assume that all platforms support the
notion of a "path" to uniquely identify a file on the system. How
-that path is actually written differs.
+that path is really written, though, differs considerably.
-While they are similar, file path specifications differ between Unix,
-Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS> and probably others.
-Unix, for example, is one of the few OSes that has the idea of a single
-root directory.
+Atlhough similar, file path specifications differ between Unix,
+Windows, S<Mac OS>, OS/2, VMS, VOS, S<RISC OS>, and probably others.
+Unix, for example, is one of the few OSes that has the elegant idea
+of a single root directory.
DOS, OS/2, VMS, VOS, and Windows can work similarly to Unix with C</>
as path separator, or in their own idiosyncratic ways (such as having
separator, or go native and use C<.> for path separator and C<:> to
signal filesystems and disk names.
-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 to be running the program.
+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
+to be running the program.
use File::Spec::Functions;
chdir(updir()); # go up one directory
# on Unix and Win32, './temp/file.txt'
# on Mac OS, ':temp:file.txt'
-File::Spec is available in the standard distribution, as of version
+File::Spec is available in the standard distribution as of version
5.004_05.
-In general, production code should not have file paths hardcoded; making
-them user supplied or from a configuration file is better, keeping in mind
-that file path syntax varies on different machines.
+In general, production code should not have file paths hardcoded.
+Making them user-supplied or read from a configuration file is
+better, keeping in mind that file path syntax varies on different
+machines.
This is especially noticeable in scripts like Makefiles and test suites,
which often assume C</> as a path separator for subdirectories.
-Also of use is File::Basename, from the standard distribution, which
+Also of use is File::Basename from the standard distribution, which
splits a pathname into pieces (base filename, full path to directory,
and file suffix).
Even when on a single platform (if you can call Unix a single platform),
-remember not to count on the existence or the contents of
+remember not to count on the existence or the contents of particular
system-specific files or directories, like F</etc/passwd>,
-F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
-example, F</etc/passwd> may exist but it may not contain the encrypted
-passwords because the system is using some form of enhanced security,
-or it may not contain all the accounts because the system is using NIS.
+F</etc/sendmail.conf>, F</etc/resolv.conf>, or even F</tmp/>. For
+example, F</etc/passwd> may exist but not contain the encrypted
+passwords, because the system is using some form of enhanced security.
+Or it may not contain all the accounts, because the system is using NIS.
If code does need to rely on such a file, include a description of the
-file and its format in the code's documentation, and make it easy for
+file and its format in the code's documentation, then make it easy for
the user to override the default location of the file.
-Don't assume a text file will end with a newline.
+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.
+portability, onerous a burden though this may appear.
-Likewise, if using the AutoSplit module, try to keep the split functions to
-8.3 naming and case-insensitive conventions; or, at the very least,
+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.
-There certainly can be whitespace in filenames on most systems, but
-some may not allow it. Many systems (DOS, VMS) cannot have more than
-one C<.> in their filenames.
+Whitespace in filenames is tolerated on most systems, but not all.
+Many systems (DOS, VMS) cannot have more than one C<.> in their filenames.
Don't assume C<E<gt>> won't be the first character of a filename.
-Always use C<E<lt>> explicitly to open a file for reading.
+Always use C<E<lt>> explicitly to open a file for reading,
+unless you want the user to be able to specify a pipe open.
open(FILE, "< $existing_file") or die $!;
If filenames might use strange characters, it is safest to open it
with C<sysopen> instead of C<open>. C<open> is magic and can
translate characters like C<E<gt>>, C<E<lt>>, and C<|>, which may
-be the wrong thing to do.
-
+be the wrong thing to do. (Sometimes, though, it's the right thing.)
=head2 System Interaction
-Not all platforms provide for the notion of a command line, necessarily.
-These are usually platforms that rely on a Graphical User Interface (GUI)
-for user interaction. So a program requiring command lines might not work
-everywhere. But this is probably for the user of the program to deal
-with, so don't stay up late worrying about it.
+Not all platforms provide a command line. These are usually platforms
+that rely primarily on a Graphical User Interface (GUI) for user
+interaction. A program requiring a command line interface might
+not work everywhere. This is probably for the user of the program
+to deal with, so don't stay up late worrying about it.
-Some platforms can't delete or rename files that are being held open by
-the system. Remember to C<close> files when you are done with them.
-Don't C<unlink> or C<rename> an open file. Don't C<tie> or C<open> a
-file that is already tied or opened; C<untie> or C<close> first.
+Some platforms can't delete or rename files held open by the system.
+Remember to C<close> files when you are done with them. Don't
+C<unlink> or C<rename> an open file. Don't C<tie> or C<open> a
+file already tied or opened; C<untie> or C<close> it first.
Don't open the same file more than once at a time for writing, as some
operating systems put mandatory locks on such files.
Don't count on specific values of C<$!>.
-
=head2 Interprocess Communication (IPC)
-In general, don't directly access the system in code that is meant to be
-portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>, C<``>,
-C<qx//>, C<open> with a C<|>, nor any of the other things that makes being
-a Unix perl hacker worth being.
+In general, don't directly access the system in code meant to be
+portable. That means, no C<system>, C<exec>, C<fork>, C<pipe>,
+C<``>, C<qx//>, C<open> with a C<|>, nor any of the other things
+that makes being a perl hacker worth being.
Commands that launch external processes are generally supported on
-most platforms (though many of them do not support any type of forking),
-but the problem with using them arises from what you invoke with them.
-External tools are often named differently on different platforms, often
-not available in the same location, often accept different arguments,
-often behave differently, and often represent their results in a
-platform-dependent way. Thus you should seldom depend on them to produce
-consistent results.
+most platforms (though many of them do not support any type of
+forking). The problem with using them arises from what you invoke
+them on. External tools are often named differently on different
+platforms, may not be available in the same location, migth accept
+different arguments, can behave differently, and often present their
+results in a platform-dependent way. Thus, you should seldom depend
+on them to produce consistent results. (Then again, if you're calling
+I<netstat -a>, you probably don't expect it to run on both Unix and CP/M.)
-One especially common bit of Perl code is opening a pipe to sendmail:
+One especially common bit of Perl code is opening a pipe to B<sendmail>:
- open(MAIL, '|/usr/lib/sendmail -t') or die $!;
+ open(MAIL, '|/usr/lib/sendmail -t')
+ or die "cannot fork sendmail: $!";
This is fine for systems programming when sendmail is known to be
available. But it is not fine for many non-Unix systems, and even
some Unix systems that may not have sendmail installed. If a portable
-solution is needed, see the C<Mail::Send> and C<Mail::Mailer> modules
-in the C<MailTools> distribution. C<Mail::Mailer> provides several
-mailing methods, including mail, sendmail, and direct SMTP
-(via C<Net::SMTP>) if a mail transfer agent is not available.
+solution is needed, see the various distributions on CPAN that deal
+with it. Mail::Mailer and Mail::Send in the MailTools distribution are
+commonly used, and provide several mailing methods, including mail,
+sendmail, and direct SMTP (via Net::SMTP) if a mail transfer agent is
+not available. Mail::Sendmail is a standalone module that provides
+simple, platform-independent mailing.
+
+The Unix System V IPC (C<msg*(), sem*(), shm*()>) is not available
+even on all Unix platforms.
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).
-The Unix System V IPC (C<msg*(), sem*(), shm*()>) is not available
-even in all Unix platforms.
-
-
=head2 External Subroutines (XS)
-XS code, in general, can be made to work with any platform; but dependent
+XS code can usually be made to work with any platform, but dependent
libraries, header files, etc., might not be readily available or
portable, or the XS code itself might be platform-specific, just as Perl
code might be. If the libraries and headers are portable, then it is
normally reasonable to make sure the XS code is portable, too.
-There is a different kind of portability issue with writing XS
-code: availability of a C compiler on the end-user's system. C brings
-with it its own portability issues, and writing XS code will expose you to
-some of those. Writing purely in perl is a comparatively easier way to
+A different type of portability issue arises when writing XS code:
+availability of a C compiler on the end-user's system. C brings
+with it its own portability issues, and writing XS code will expose
+you to some of those. Writing purely in Perl is an easier way to
achieve portability.
-
=head2 Standard Modules
In general, the standard modules work across platforms. Notable
programs that may not be available), platform-specific modules (like
ExtUtils::MM_VMS), and DBM modules.
-There is no one DBM module that is available on all platforms.
+There is no one DBM module available on all platforms.
SDBM_File and the others are generally available on all Unix and DOSish
ports, but not in MacPerl, where only NBDM_File and DB_File are
available.
The good news is that at least some DBM module should be available, and
AnyDBM_File will use whichever module it can find. Of course, then
-the code needs to be fairly strict, dropping to the lowest common
-denominator (e.g., not exceeding 1K for each record), so that it will
+the code needs to be fairly strict, dropping to the greatest common
+factor (e.g., not exceeding 1K for each record), so that it will
work with any DBM module. See L<AnyDBM_File> for more details.
-
=head2 Time and Date
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}>,
+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.
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;
$offset = Time::Local::timegm(0, 0, 0, 1, 0, 70);
+
The value for C<$offset> in Unix will be C<0>, but in Mac OS will be
some large number. C<$offset> can then be added to a Unix time value
to get what should be the proper value on any system.
=head2 Character sets and character encoding
-Assume very little about character sets. Do not assume anything about
-the numerical values (C<ord>, C<chr>) of characters. Do not
+Assume little about character sets. Assume nothing about
+numerical values (C<ord>, C<chr>) of characters. Do not
assume that the alphabetic characters are encoded contiguously (in
-numerical sense). Do not assume anything about the ordering of the
+the numeric sense). Do not assume anything about the ordering of the
characters. The lowercase letters may come before or after the
-uppercase letters, the lowercase and uppercase may be interlaced so
-that both 'a' and 'A' come before the 'b', the accented and other
+uppercase letters; the lowercase and uppercase may be interlaced so
+that both `a' and `A' come before `b'; the accented and other
international characters may be interlaced so that E<auml> comes
-before the 'b'.
-
+before `b'.
=head2 Internationalisation
-If you may assume POSIX (a rather large assumption, that in practice
-means Unix), you may read more about the POSIX locale system from
-L<perllocale>. The locale system at least attempts to make things a
-little bit more portable, or at least more convenient and
-native-friendly for non-English users. The system affects character
-sets and encoding, and date and time formatting, among other things.
-
+If you may assume POSIX (a rather large assumption), you may read
+more about the POSIX locale system from L<perllocale>. The locale
+system at least attempts to make things a little bit more portable,
+or at least more convenient and native-friendly for non-English
+users. The system affects character sets and encoding, and date
+and time formatting--amongst other things.
=head2 System Resources
while (<FILE>) {$file .= $_} # sometimes bad
$file = join('', <FILE>); # better
-The last two may appear unintuitive to most people. The first of those
-two constructs repeatedly grows a string, while the second allocates a
-large chunk of memory in one go. On some systems, the latter is more
-efficient that the former.
-
+The last two constructs may appear unintuitive to most people. The
+first repeatedly grows a string, whereas the second allocates a
+large chunk of memory in one go. On some systems, the second is
+more efficient that the first.
=head2 Security
-Most multi-user platforms provide basic levels of security that is usually
-felt at the file-system level. Other platforms usually don't
-(unfortunately). Thus the notion of user id, or "home" directory, or even
-the state of being logged-in, may be unrecognizable on many platforms. If
-you write programs that are security-conscious, it is usually best to know
-what type of system you will be operating under, and write code explicitly
-for that platform (or class of platforms).
-
+Most multi-user platforms provide basic levels of security, usually
+implemented at the filesystem level. Some, however, do
+not--unfortunately. Thus the notion of user id, or "home" directory,
+or even the state of being logged-in, may be unrecognizable on many
+platforms. If you write programs that are security-conscious, it
+is usually best to know what type of system you will be running
+under so that you can write code explicitly for that platform (or
+class of platforms).
=head2 Style
variable C<$^O> to differentiate platforms, as described in
L<"PLATFORMS">.
-Be careful in the tests you supply with your module or programs. Often
-module code is fully portable, but the tests are not. This occurs
-often 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 an C<eval>. 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.
-
- $@ =~ /^I got an error!/ # may fail
- $@ =~ /I got an error!/ # probably better
-
+Be careful in the tests you supply with your module or programs.
+Module code may be fully portable, but its tests might not be. This
+often happens when tests spawn off other processes or call external
+programs to aid in the testing, or when (as noted above) the tests
+assume certain things about the filesystem and paths. Be careful
+not to depend on a specific output style for errors, such as when
+checking C<$!> after an 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.
=head1 CPAN Testers
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 or not
+platforms; two, to provide users with information about whether
a given module works on a given platform.
=over 4
=back
-
=head1 PLATFORMS
As of version 5.002, Perl is built with a C<$^O> variable that
indicates the operating system it was built on. This was implemented
-to help speed up code that would otherwise have to C<use Config;> and
-use the value of C<$Config{'osname'}>. Of course, to get
+to help speed up code that would otherwise have to C<use Config>
+and use the value of C<$Config{osname}>. Of course, to get more
detailed information about the system, looking into C<%Config> is
certainly recommended.
-C<%Config> cannot always be trusted, however,
-because it is built at compile time, and if perl was built in once
-place and transferred elsewhere, some values may be off, or the
-values may have been edited after the fact.
-
+C<%Config> 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.
=head2 Unix
at the shell prompt. Here, for example, are a few of the more popular
Unix flavors:
- uname $^O $Config{'archname'}
+ uname $^O $Config{'archname'}
--------------------------------------------
- AIX aix aix
+ AIX aix aix
BSD/OS bsdos i386-bsdos
dgux dgux AViiON-dgux
DYNIX/ptx dynixptx i386-dynixptx
- FreeBSD freebsd freebsd-i386
- Linux linux i386-linux
+ FreeBSD freebsd freebsd-i386
+ Linux linux i386-linux
Linux linux i586-linux
Linux linux ppc-linux
- HP-UX hpux PA-RISC1.1
- IRIX irix irix
+ HP-UX hpux PA-RISC1.1
+ IRIX irix irix
openbsd openbsd i386-openbsd
- OSF1 dec_osf alpha-dec_osf
+ OSF1 dec_osf alpha-dec_osf
reliantunix-n svr4 RM400-svr4
SCO_SV sco_sv i386-sco_sv
SINIX-N svr4 RM400-svr4
sn4609 unicos CRAY_C90-unicos
sn6521 unicosmk t3e-unicosmk
sn9617 unicos CRAY_J90-unicos
- SunOS solaris sun4-solaris
- SunOS solaris i86pc-solaris
- SunOS4 sunos sun4-sunos
-
-Note that because the C<$Config{'archname'}> may depend on the hardware
-architecture it may vary quite a lot, much more than the C<$^O>.
+ SunOS solaris sun4-solaris
+ SunOS solaris i86pc-solaris
+ SunOS4 sunos sun4-sunos
+Because the value of C<$Config{archname}> may depend on the
+hardware architecture, it can vary more than the value of C<$^O>.
=head2 DOS and Derivatives
-Perl has long been ported to PC style microcomputers running under
+Perl has long been ported to Intel-style microcomputers running under
systems like PC-DOS, MS-DOS, OS/2, and most Windows platforms you can
bring yourself to mention (except for Windows CE, if you count that).
-Users familiar with I<COMMAND.COM> and/or I<CMD.EXE> style shells should
+Users familiar with I<COMMAND.COM> or I<CMD.EXE> style shells should
be aware that each of these file specifications may have subtle
differences:
$filespec2 = 'c:\foo\bar\file.txt';
$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 the option
-prefix, so they may get confused by filenames containing C</>. Aside
-from calling any external programs, C</> 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.
+System calls accept either C</> or C<\> as the path separator.
+However, many command-line utilities of DOS vintage treat C</> as
+the option prefix, so may get confused by filenames containing C</>.
+Aside from calling any external programs, C</> 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.
-The DOS FAT filesystem can only accommodate "8.3" style filenames. Under
-the "case insensitive, but case preserving" HPFS (OS/2) and NTFS (NT)
+The DOS FAT filesystem can accommodate only "8.3" style filenames. Under
+the "case-insensitive, but case-preserving" HPFS (OS/2) and NTFS (NT)
filesystems you may have to be careful about case returned with functions
like C<readdir> or used with functions like C<open> or C<opendir>.
-DOS also treats several filenames as special, such as AUX, PRN, NUL, CON,
-COM1, LPT1, LPT2 etc. Unfortunately these filenames won't even work
-if you include an explicit directory prefix, in some cases. It is best
-to avoid such filenames, if you want your code to be portable to DOS
-and its derivatives.
+DOS also treats several filenames as special, such as AUX, PRN,
+NUL, CON, COM1, LPT1, LPT2, 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 DOS and its derivatives. It's hard to know what
+these all are, unfortunately.
Users of these operating systems may also wish to make use of
-scripts such as F<pl2bat.bat> or F<pl2cmd> as appropriate to
+scripts such as I<pl2bat.bat> or I<pl2cmd> to
put wrappers around your scripts.
Newline (C<\n>) is translated as C<\015\012> by STDIO when reading from
and writing to files (see L<"Newlines">). C<binmode(FILEHANDLE)>
will keep C<\n> translated as C<\012> for that filehandle. Since it is a
no-op on other systems, C<binmode> should be used for cross-platform code
-that deals with binary data.
+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.
-The C<$^O> variable and the C<$Config{'archname'}> values for various
+The C<$^O> variable and the C<$Config{archname}> values for various
DOSish perls are as follows:
OS $^O $Config{'archname'}
=back
-
=head2 S<Mac OS>
Any module requiring XS compilation is right out for most people, because
:file for relative pathnames
file for relative pathnames
-Files in a directory are stored in alphabetical order. Filenames are
+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 path separator.
+null and C<:>, which is reserved as the path separator.
Instead of C<flock>, see C<FSpSetFLock> and C<FSpRstFLock> in the
Mac::Files module, or C<chmod(0444, ...)> and C<chmod(0666, ...)>.
@ARGV = split /\s+/, MacPerl::Ask('Arguments?');
}
-A MacPerl script saved as a droplet will populate C<@ARGV> with the full
+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 use programs on a kind of command line 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:
+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
may run a slightly modified version of MacPerl, using the Carbon interfaces.
S<Mac OS X Server> and its Open Source version, Darwin, both run Unix
-perl natively (with a small number of patches). Full support for these
+perl natively (with a few patches). Full support for these
is slated for perl5.006.
-
Also see:
=over 4
=back
-
=head2 VMS
Perl on VMS is discussed in F<vms/perlvms.pod> in the perl distribution.
-Note that perl on VMS can accept either VMS- or Unix-style file
+Perl on VMS can accept either VMS- or Unix-style file
specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" SYS$LOGIN:LOGIN.COM
$ perl -e "print ""Hello, world.\n"""
Hello, world.
-There are a number of ways to wrap your perl scripts in DCL .COM files if
+There are several ways to wrap your perl scripts in DCL F<.COM> files, if
you are so inclined. For example:
$ write sys$output "Hello from DCL!"
extensions is also 39 characters. Version is a number from 1 to
32767. Valid characters are C</[A-Z0-9$_-]/>.
-VMS' RMS filesystem is case insensitive and does not preserve case.
+VMS's RMS filesystem is case-insensitive and does not preserve case.
C<readdir> returns lowercased filenames, but specifying a file for
-opening remains case insensitive. Files without extensions have a
+opening remains case-insensitive. Files without extensions have a
trailing period on them, so doing a C<readdir> with a file named F<A.;5>
will return F<a.> (though that file could be opened with
C<open(FH, 'A')>).
non-VMS platforms and can be helpful for conversions to and from RMS
native formats.
-What C<\n> represents depends on the type of file that is open. It could
+What C<\n> represents depends on the type of file opened. It could
be C<\015>, C<\012>, C<\015\012>, or nothing. Reading from a file
translates newlines to C<\012>, unless C<binmode> was executed on that
handle, just like DOSish perls.
print "I'm not so sure about where $^O is...\n";
}
-On VMS perl determines the UTC offset from the C<SYS$TIMEZONE_DIFFERENTIAL>
-logical name. Though the VMS epoch began at 17-NOV-1858 00:00:00.00,
+On VMS, perl determines the UTC offset from the C<SYS$TIMEZONE_DIFFERENTIAL>
+logical name. Although the VMS epoch began at 17-NOV-1858 00:00:00.00,
calls to C<localtime> are adjusted to count offsets from
-01-JAN-1970 00:00:00.00 just like Unix.
+01-JAN-1970 00:00:00.00, just like Unix.
Also see:
=back
-
=head2 VOS
Perl on VOS is discussed in F<README.vos> in the perl distribution.
-Note that perl on VOS can accept either VOS- or Unix-style file
+Perl on VOS can accept either VOS- or Unix-style file
specifications as in either of the following:
$ perl -ne "print if /perl_setup/i" >system>notices
$ perl -ne "print if /perl_setup/i" >system/notices
-Note that even though VOS allows the slash character to appear in object
+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
=back
-
=head2 EBCDIC Platforms
Recent versions of Perl have been ported to platforms such as OS/400 on
AS/400 minicomputers as well as OS/390 & VM/ESA for IBM Mainframes. Such
computers use EBCDIC character sets internally (usually Character Code
-Set ID 00819 for OS/400 and IBM-1047 for OS/390 & VM/ESA). Note that on
+Set ID 00819 for OS/400 and IBM-1047 for OS/390 & VM/ESA). On
the mainframe perl currently works under the "Unix system services
for OS/390" (formerly known as OpenEdition) and VM/ESA OpenEdition.
print "Hello from perl!\n";
-On the AS/400, assuming that PERL5 is in your library list, you may need
+On the AS/400, if PERL5 is in your library list, you may need
to wrap your perl scripts in a CL procedure to invoke them like so:
BEGIN
and C<|>, not to mention dealing with socket interfaces to ASCII computers
(see L<"Newlines">).
-Fortunately, most web servers for the mainframe will correctly translate
-the C<\n> in the following statement to its ASCII equivalent (note that
-C<\r> is the same under both Unix and OS/390 & VM/ESA):
+Fortunately, most web servers for the mainframe will correctly
+translate the C<\n> in the following statement to its ASCII equivalent
+(C<\r> is the same under both Unix and OS/390 & VM/ESA):
print "Content-type: text/html\r\n\r\n";
if (chr(169) eq 'z') { print "EBCDIC may be spoken here!\n"; }
-Note that one thing you may not want to rely on is the EBCDIC encoding
+One thing you may not want to rely on is the EBCDIC encoding
of punctuation characters since these may differ from code page to code
page (and once your module or script is rumoured to work with EBCDIC,
folks will want it to work with all EBCDIC character sets).
=back
-
=head2 Acorn RISC OS
-As Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
-Unix and Unix filename emulation is turned on by default, it is quite
-likely that most simple scripts will work "out of the box". The native
+Because Acorns use ASCII with newlines (C<\n>) in text files as C<\012> like
+Unix, and because Unix filename emulation is turned on by default,
+most simple scripts will probably work "out of the box". The native
filesystem is modular, and individual filesystems are free to be
case-sensitive or insensitive, and are usually case-preserving. Some
-native filesystems have name length limits which file and directory
+native filesystems have name length limits, which file and directory
names are silently truncated to fit. Scripts should be aware that the
standard filesystem currently has a name length limit of B<10>
characters, with up to 77 items in a directory, but other filesystems
foul of the C<$.> if scripts are not careful.
Logical paths specified by system variables containing comma-separated
-search lists are also allowed, hence C<System:Modules> is a valid
+search lists are also allowed; hence C<System:Modules> is a valid
filename, and the filesystem will prefix C<Modules> with each section of
C<System$Path> until a name is made that points to an object on disk.
-Writing to a new file C<System:Modules> would only be allowed if
+Writing to a new file C<System:Modules> would be allowed only if
C<System$Path> contains a single item list. The filesystem will also
expand system variables in filenames if enclosed in angle brackets, so
C<E<lt>System$DirE<gt>.Modules> would look for the file
be assumed to be unique after 10 characters, Acorn implemented the C
compiler to strip the trailing C<.c> C<.h> C<.s> and C<.o> suffix from
filenames specified in source code and store the respective files in
-subdirectories named after the suffix. Hence files are translated:
+subdirectories named after the suffix. Hence files are translated:
foo.h h.foo
C:foo.h C:h.foo (logical path variable)
11charname_.c c.11charname (assuming filesystem truncates at 10)
The Unix emulation library's translation of filenames to native assumes
-that this sort of translation is required, and allows a user defined list
-of known suffixes which it will transpose in this fashion. This may
-appear transparent, but consider that with these rules C<foo/bar/baz.h>
+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<foo/bar/baz.h>
and C<foo/bar/h/baz> both map to C<foo.bar.h.baz>, and that C<readdir> and
C<glob> cannot and do not attempt to emulate the reverse mapping. Other
C<.>'s in filenames are translated to C</>.
-As implied above the environment accessed through C<%ENV> is global, and
+As implied above, the environment accessed through C<%ENV> is global, and
the convention is that program specific environment variables are of the
form C<Program$Name>. Each filesystem maintains a current directory,
and the current filesystem's current directory is the B<global> current
-directory. Consequently, sociable scripts don't change the current
-directory but rely on full pathnames, and scripts (and Makefiles) cannot
+directory. Consequently, sociable programs don't change the current
+directory but rely on full pathnames, and programs (and Makefiles) cannot
assume that they can spawn a child process which can change the current
directory without affecting its parent (and everyone else for that
matter).
-As native operating system filehandles are global and currently are
-allocated down from 255, with 0 being a reserved value the Unix emulation
+Because native operating system filehandles are global and are currently
+allocated down from 255, with 0 being a reserved value, the Unix emulation
library emulates Unix filehandles. Consequently, you can't rely on
passing C<STDIN>, C<STDOUT>, or C<STDERR> to your children.
Unix tools being available, or that any tools found have Unix-like command
line arguments.
-Extensions and XS are, in theory, buildable by anyone using free tools.
-In practice, many don't, as users of the Acorn platform are used to binary
-distribution. MakeMaker does run, but no available make currently copes
-with MakeMaker's makefiles; even if/when this is fixed, the lack of a
-Unix-like shell can cause problems with makefile rules, especially lines
-of the form C<cd sdbm && make all>, and anything using quoting.
+Extensions and XS are, in theory, buildable by anyone using free
+tools. In practice, many don't, as users of the Acorn platform are
+used to binary distributions. MakeMaker does run, but no available
+make currently copes with MakeMaker's makefiles; even if and when
+this should be fixed, the lack of a Unix-like shell will cause
+problems with makefile rules, especially lines of the form C<cd
+sdbm && make all>, and anything using quoting.
"S<RISC OS>" is the proper name for the operating system, but the value
in C<$^O> is "riscos" (because we don't like shouting).
-
=head2 Other perls
-Perl has been ported to a variety of platforms that do not fit into any of
-the above categories. 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<ports/> directory on CPAN for
-information, and possibly binaries, for the likes of: aos, Atari ST, lynxos,
-riscos, Novell Netware, Tandem Guardian, I<etc.> (yes we know that some of
-these OSes may fall under the Unix category, but we are not a standards body.)
+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<ports/> directory on CPAN for information, and possibly binaries,
+for the likes of: aos, Atari ST, lynxos, riscos, Novell Netware,
+Tandem Guardian, I<etc.> (Yes, we know that some of these OSes may
+fall under the Unix category, but we are not a standards body.)
See also:
=back
-
=head1 FUNCTION IMPLEMENTATIONS
-Listed below are functions unimplemented or implemented differently on
-various platforms. Following each description will be, in parentheses, a
-list of platforms that the description applies to.
+Listed below are functions that are either completely unimplemented
+or else have been implemented differently on various platforms.
+Following each description will be, in parentheses, a list of
+platforms that the description applies to.
-The list may very well be incomplete, or wrong in some places. When in
-doubt, consult the platform-specific README files in the Perl source
-distribution, and other documentation resources for a given port.
+The list may well be incomplete, or even wrong in some places. When
+in doubt, consult the platform-specific README files in the Perl
+source distribution, and any other documentation resources accompanying
+a given port.
Be aware, moreover, that even among Unix-ish systems there are variations.
-For many functions, you can also query C<%Config>, exported by default
-from the Config module. For example, to check if the platform has the C<lstat>
-call, check C<$Config{'d_lstat'}>. See L<Config> for a full
-description of available variables.
-
+For many functions, you can also query C<%Config>, exported by
+default from the Config module. For example, to check whether the
+platform has the C<lstat> call, check C<$Config{d_lstat}>. See
+L<Config> for a full description of available variables.
=head2 Alphabetical Listing of Perl Functions
=item -X
-C<-r>, C<-w>, and C<-x> have only a very limited meaning; directories
+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<Mac OS>)
+considerations. C<-o> is not supported. (S<Mac OS>)
-C<-r>, C<-w>, C<-x>, and C<-o> tell whether or not file is accessible,
-which may not reflect UIC-based file protections. (VMS)
+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<Mac OS>).
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<RISC OS>)
+current size. (S<RISC OS>)
C<-R>, C<-W>, C<-X>, C<-O> are indistinguishable from C<-r>, C<-w>,
C<-x>, C<-o>. (S<Mac OS>, Win32, VMS, S<RISC OS>)
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<Mac OS> often. (S<Mac OS>)
+affect S<Mac OS> often. (S<Mac OS>)
C<-x> (or C<-X>) determine if a file ends in one of the executable
-suffixes. C<-S> is meaningless. (Win32)
+suffixes. C<-S> is meaningless. (Win32)
C<-x> (or C<-X>) determine if a file has an executable file type.
(S<RISC OS>)
=item binmode FILEHANDLE
-Meaningless. (S<Mac OS>, S<RISC OS>)
+Meaningless. (S<Mac OS>, S<RISC OS>)
Reopens file and restores pointer; if function fails, underlying
filehandle may be closed, or pointer may be in a different position.
=item chmod LIST
-Only limited meaning. Disabling/enabling write permission is mapped to
+Only limited meaning. Disabling/enabling write permission is mapped to
locking/unlocking the file. (S<Mac OS>)
Only good for changing "owner" read-write access, "group", and "other"
Globbing built-in, but only C<*> and C<?> metacharacters are supported.
(S<Mac OS>)
-Features depend on external perlglob.exe or perlglob.bat. May be
+Features depend on external perlglob.exe or perlglob.bat. May be
overridden with something like File::DosGlob, which is recommended.
(Win32)
=item open FILEHANDLE
-The C<|> variants are only supported if ToolServer is installed.
+The C<|> variants are supported only if ToolServer is installed.
(S<Mac OS>)
open to C<|-> and C<-|> are unsupported. (S<Mac OS>, Win32, S<RISC OS>)
Only implemented if ToolServer is installed. (S<Mac OS>)
As an optimization, may not call the command shell specified in
-C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
+C<$ENV{PERL5SHELL}>. C<system(1, @args)> spawns an external
process and immediately returns its process designator, without
waiting for it to terminate. Return value may be used subsequently
in C<wait> or C<waitpid>. (Win32)
Returns undef where unavailable, as of version 5.005.
-C<umask()> works but the correct permissions are only set when the file
-is finally close()d. (AmigaOS)
+C<umask> works but the correct permissions are set only when the file
+is finally closed. (AmigaOS)
=item utime LIST
=over 4
+=item v1.43, 24 May 1999
+
+Added a lot of cleaning up from Tom Christiansen.
+
=item v1.42, 22 May 1999
+
Added notes about tests, sprintf/printf, and epoch offsets.
+
=item v1.41, 19 May 1999
Lots more little changes to formatting and content.
=head1 VERSION
-Version 1.42, last modified 22 May 1999
+Version 1.43, last modified 24 May 1999
projects / p5sagit/p5-mst-13.2.git / commitdiff