X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlport.pod;h=ef05ecf3492c94d774ff5532fc5213618631cf54;hb=666f95b95a2f6347f7b7bbc8951144df2db05479;hp=a2133484dd79658fb103113062b5b260ca7c8a6d;hpb=9d6eb86e4075182b9cda16d90e5d387c1537d687;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlport.pod b/pod/perlport.pod index a213348..ef05ecf 100644 --- a/pod/perlport.pod +++ b/pod/perlport.pod @@ -232,6 +232,9 @@ binary, or else consider using modules like Data::Dumper (included in the standard distribution as of Perl 5.005) and Storable (included as of perl 5.8). Keeping all data as text significantly simplifies matters. +The v-strings are portable only up to v2147483647 (0x7FFFFFFF), that's +how far EBCDIC, or more precisely UTF-EBCDIC will go. + =head2 Files and Filesystems Most platforms these days structure files in a hierarchical fashion. @@ -259,6 +262,9 @@ timestamp (meaning that about the only portable timestamp is the modification timestamp), or one second granularity of any timestamps (e.g. the FAT filesystem limits the time granularity to two seconds). +The "inode change timestamp" (the <-C> filetest) may really be the +"creation timestamp" (which it is not in UNIX). + VOS perl can emulate Unix filenames with C as path separator. The native pathname characters greater-than, less-than, number-sign, and percent-sign are always accepted. @@ -318,30 +324,61 @@ the user to override the default location of the file. 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 and F, as many platforms have case-insensitive -filenames. Also, try not to have non-word characters (except for C<.>) -in the names, and keep them to the 8.3 convention, for maximum -portability, onerous a burden though this may appear. +Do not have two files or directories of the same name with different +case, like F and F, as many platforms have +case-insensitive (or at least case-forgiving) filenames. Also, try +not to have non-word characters (except for C<.>) in the names, and +keep them to the 8.3 convention, for maximum portability, onerous a +burden though this may appear. Likewise, when using the AutoSplit module, try to keep your functions to 8.3 naming and case-insensitive conventions; or, at the least, make it so the resulting files have a unique (case-insensitively) first 8 characters. -Whitespace in filenames is tolerated on most systems, but not all. +Whitespace in filenames is tolerated on most systems, but not all, +and even on systems where it might be tolerated, some utilities +might become confused by such whitespace. + Many systems (DOS, VMS) cannot have more than one C<.> in their filenames. Don't assume C<< > >> won't be the first character of a filename. -Always use C<< < >> explicitly to open a file for reading, -unless you want the user to be able to specify a pipe open. +Always use C<< < >> explicitly to open a file for reading, or even +better, use the three-arg version of open, unless you want the user to +be able to specify a pipe open. - open(FILE, "< $existing_file") or die $!; + open(FILE, '<', $existing_file) or die $!; If filenames might use strange characters, it is safest to open it with C instead of C. C is magic and can translate characters like C<< > >>, C<< < >>, and C<|>, which may be the wrong thing to do. (Sometimes, though, it's the right thing.) +Three-arg open can also help protect against this translation in cases +where it is undesirable. + +Don't use C<:> as a part of a filename since many systems use that for +their own semantics (MacOS Classic for separating pathname components, +many networking schemes and utilities for separating the nodename and +the pathname, and so on). For the same reasons, avoid C<@>, C<;> and +C<|>. + +Don't assume that in pathnames you can collapse two leading slashes +C into one: some networking and clustering filesystems have special +semantics for that. Let the operating system to sort it out. + +The I as defined by ANSI C are + + a b c d e f g h i j k l m n o p q r t u v w x y z + A B C D E F G H I J K L M N O P Q R T U V W X Y Z + 0 1 2 3 4 5 6 7 8 9 + . _ - + +and the "-" shouldn't be the first character. If you want to be +hypercorrect, stay case-insensitive and within the 8.3 naming +convention (all the files and directories have to be unique within one +directory if their names are lowercased and truncated to eight +characters before the C<.>, if any, and to three characters after the +C<.>, if any). (And do not use C<.>s in directory names.) =head2 System Interaction @@ -502,15 +539,20 @@ to get what should be the proper value on any system. =head2 Character sets and character encoding -Assume little about character sets. Assume nothing about -numerical values (C, C) of characters. Do not -assume that the alphabetic characters are encoded contiguously (in -the numeric sense). Do not assume anything about the ordering of the -characters. The lowercase letters may come before or after the -uppercase letters; the lowercase and uppercase may be interlaced so -that both `a' and `A' come before `b'; the accented and other -international characters may be interlaced so that E comes -before `b'. +Assume very little about character sets. + +Assume nothing about numerical values (C, C) of characters. +Do not use explicit code point ranges (like \xHH-\xHH); use for +example symbolic character classes like C<[:print:]>. + +Do not assume that the alphabetic characters are encoded contiguously +(in the numeric sense). There may be gaps. + +Do not assume anything about the ordering of the characters. +The lowercase letters may come before or after the uppercase letters; +the lowercase and uppercase may be interlaced so that both `a' and `A' +come before `b'; the accented and other international characters may +be interlaced so that E comes before `b'. =head2 Internationalisation @@ -638,6 +680,7 @@ are a few of the more popular Unix flavors: -------------------------------------------- AIX aix aix BSD/OS bsdos i386-bsdos + Darwin darwin darwin dgux dgux AViiON-dgux DYNIX/ptx dynixptx i386-dynixptx FreeBSD freebsd freebsd-i386 @@ -1397,6 +1440,9 @@ Only good for changing "owner" and "other" read-write access. (S) 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 Not implemented. (S, Win32, Plan9, S, VOS) @@ -1747,7 +1793,11 @@ as '', so numeric comparison or manipulation of these fields may cause 'not numeric' warnings. mtime and atime are the same thing, and ctime is creation time instead of -inode change time. (S) +inode change time. (S). + +ctime not supported on UFS (S). + +ctime is creation time instead of inode change time (Win32). device and inode are not meaningful. (Win32) @@ -1780,13 +1830,13 @@ OS>, OS/390, VM/ESA) =item system LIST In general, do not assume the UNIX/POSIX semantics that you can shift -the C<$?> left by eight to get the exit value, or that C<$? & 127> +C<$?> right by eight to get the exit value, or that C<$? & 127> would give you the number of the signal that terminated the program, or that C<$? & 128> would test true if the program was terminated by a coredump. Instead, use the POSIX W*() interfaces: for example, use WIFEXITED($?) an WEXITVALUE($?) to test for a normal exit and the exit value, and WIFSIGNALED($?) and WTERMSIG($?) for a signal exit and the -signal. Core dumping is not a portable concept so there's no portable +signal. Core dumping is not a portable concept, so there's no portable way to test for that. Only implemented if ToolServer is installed. (S) @@ -2152,7 +2202,7 @@ Andrew M. Langmead , Larry Moore , Paul Moore , Chris Nandor , -Matthias Neeracher , +Matthias Neeracher , Philip Newton , Gary Ng <71564.1743@CompuServe.COM>, Tom Phoenix , @@ -2165,6 +2215,3 @@ Michael G Schwern , Dan Sugalski , Nathan Torkington . -=head1 VERSION - -Version 1.50, last modified 10 Jul 2001