X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=lib%2FPerlIO.pm;h=c0acdec4a4557a39468d62986262439eb4cd10fc;hb=584420f022db57225e9644b9c6668ff9f567984a;hp=1ee5b8881548cdeb25b3a63397047cf608fe2109;hpb=4ec2216f20a53a69267b31ce136e7410687cbe32;p=p5sagit%2Fp5-mst-13.2.git diff --git a/lib/PerlIO.pm b/lib/PerlIO.pm index 1ee5b88..c0acdec 100644 --- a/lib/PerlIO.pm +++ b/lib/PerlIO.pm @@ -1,6 +1,6 @@ package PerlIO; -our $VERSION = '1.01'; +our $VERSION = '1.04'; # Map layer name to package that defines it our %alias; @@ -24,6 +24,8 @@ sub import } } +sub F_UTF8 () { 0x8000 } + 1; __END__ @@ -33,7 +35,7 @@ PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space =head1 SYNOPSIS - open($fh,"<:crlf", "my.txt"); # portably open a text file for reading + open($fh,"<:crlf", "my.txt"); # support platform-native and CRLF text files open($fh,"<","his.jpg"); # portably open a binary file for reading binmode($fh); @@ -59,32 +61,67 @@ The following layers are currently defined: =over 4 -=item unix +=item :unix -Low level layer which calls C, C and C etc. +Lowest level layer which provides basic PerlIO operations in terms of +UNIX/POSIX numeric file descriptor calls +(open(), read(), write(), lseek(), close()). -=item stdio +=item :stdio Layer which calls C, C and C/C etc. Note that as this is "real" stdio it will ignore any layers beneath it and got straight to the operating system via the C library as usual. -=item perlio +=item :perlio + +A from scratch implementation of buffering for PerlIO. Provides fast +access to the buffer for C which implements perl's readline/EE +and in general attempts to minimize data copying. + +C<:perlio> will insert a C<:unix> layer below itself to do low level IO. + +=item :crlf + +A layer that implements DOS/Windows like CRLF line endings. On read +converts pairs of CR,LF to a single "\n" newline character. On write +converts each "\n" to a CR,LF pair. Note that this layer likes to be +one of its kind: it silently ignores attempts to be pushed into the +layer stack more than once. + +It currently does I mimic MS-DOS as far as treating of Control-Z +as being an end-of-file marker. + +(Gory details follow) To be more exact what happens is this: after +pushing itself to the stack, the C<:crlf> layer checks all the layers +below itself to find the first layer that is capable of being a CRLF +layer but is not yet enabled to be a CRLF layer. If it finds such a +layer, it enables the CRLFness of that other deeper layer, and then +pops itself off the stack. If not, fine, use the one we just pushed. + +The end result is that a C<:crlf> means "please enable the first CRLF +layer you can find, and if you can't find one, here would be a good +spot to place a new one." + +Based on the C<:perlio> layer. + +=item :mmap -This is a re-implementation of "stdio-like" buffering written as a -PerlIO "layer". As such it will call whatever layer is below it for -its operations. +A layer which implements "reading" of files by using C to +make (whole) file appear in the process's address space, and then +using that as PerlIO's "buffer". This I be faster in certain +circumstances for large files, and may result in less physical memory +use when multiple processes are reading the same file. -=item crlf +Files which are not C-able revert to behaving like the C<:perlio> +layer. Writes also behave like C<:perlio> layer as C for write +needs extra house-keeping (to extend the file) which negates any advantage. -A layer which does CRLF to "\n" translation distinguishing "text" and -"binary" files in the manner of MS-DOS and similar operating systems. -(It currently does I mimic MS-DOS as far as treating of Control-Z -as being an end-of-file marker.) +The C<:mmap> layer will not exist if platform does not support C. -=item utf8 +=item :utf8 -Declares that the stream accepts perl's internal encoding of +Declares that the stream accepts perl's I encoding of characters. (Which really is UTF-8 on ASCII machines, but is UTF-EBCDIC on EBCDIC machines.) This allows any character perl can represent to be read from or written to the stream. The UTF-X encoding @@ -102,7 +139,7 @@ and then read it back in. $in = ; close(F); -=item bytes +=item :bytes This is the inverse of C<:utf8> layer. It turns off the flag on the layer below so that data read from it is considered to @@ -110,30 +147,36 @@ be "octets" i.e. characters in range 0..255 only. Likewise on output perl will warn if a "wide" character is written to a such a stream. -=item raw +=item :raw The C<:raw> layer is I as being identical to calling -C - the stream is made suitable for passing binary -data i.e. each byte is passed as-is. The stream will still be -buffered. Unlike earlier versions of perl C<:raw> is I just the -inverse of C<:crlf> - other layers which would affect the binary nature of -the stream are also removed or disabled. +C - the stream is made suitable for passing binary data +i.e. each byte is passed as-is. The stream will still be +buffered. + +In Perl 5.6 and some books the C<:raw> layer (previously sometimes also +referred to as a "discipline") is documented as the inverse of the +C<:crlf> layer. That is no longer the case - other layers which would +alter binary nature of the stream are also disabled. If you want UNIX +line endings on a platform that normally does CRLF translation, but still +want UTF-8 or encoding defaults the appropriate thing to do is to add +C<:perlio> to PERLIO environment variable. The implementation of C<:raw> is as a pseudo-layer which when "pushed" pops itself and then any layers which do not declare themselves as suitable for binary data. (Undoing :utf8 and :crlf are implemented by clearing -flags rather than poping layers but that is an implementation detail.) +flags rather than popping layers but that is an implementation detail.) As a consequence of the fact that C<:raw> normally pops layers -it usually only makes sense to have it as the only or first element in a -layer specification. When used as the first element it provides +it usually only makes sense to have it as the only or first element in +a layer specification. When used as the first element it provides a known base on which to build e.g. open($fh,":raw:utf8",...) will construct a "binary" stream, but then enable UTF-8 translation. -=item pop +=item :pop A pseudo layer that removes the top-most layer. Gives perl code a way to manipulate the layer stack. Should be considered @@ -145,10 +188,41 @@ An example of a possible use might be: ... binmode($fh,":encoding(...)"); # next chunk is encoded ... - binmode($fh,":pop"); # back to un-encocded + binmode($fh,":pop"); # back to un-encoded A more elegant (and safer) interface is needed. +=item :win32 + +On Win32 platforms this I layer uses native "handle" IO +rather than unix-like numeric file descriptor layer. Known to be +buggy as of perl 5.8.2. + +=back + +=head2 Custom Layers + +It is possible to write custom layers in addition to the above builtin +ones, both in C/XS and Perl. Two such layers (and one example written +in Perl using the latter) come with the Perl distribution. + +=over 4 + +=item :encoding + +Use C<:encoding(ENCODING)> either in open() or binmode() to install +a layer that does transparently character set and encoding transformations, +for example from Shift-JIS to Unicode. Note that under C +an C<:encoding> also enables C<:utf8>. See L +for more information. + +=item :via + +Use C<:via(MODULE)> either in open() or binmode() to install a layer +that does whatever transformation (for example compression / +decompression, encryption / decryption) to the filehandle. +See L for more information. + =back =head2 Alternatives to raw @@ -177,7 +251,7 @@ translation for text files then the default layers are : level layer.) Otherwise if C found out how to do "fast" IO using system's -stdio, then the default layers are : +stdio, then the default layers are: unix stdio @@ -188,8 +262,8 @@ Otherwise the default layers are These defaults may change once perlio has been better tested and tuned. The default can be overridden by setting the environment variable -PERLIO to a space separated list of layers (unix or platform low level -layer is always pushed first). +PERLIO to a space separated list of layers (C or platform low +level layer is always pushed first). This can be used to see the effect of/bugs in the various layers e.g. @@ -197,13 +271,70 @@ This can be used to see the effect of/bugs in the various layers e.g. PERLIO=stdio ./perl harness PERLIO=perlio ./perl harness +For the various value of PERLIO see L. + +=head2 Querying the layers of filehandles + +The following returns the B of the PerlIO layers on a filehandle. + + my @layers = PerlIO::get_layers($fh); # Or FH, *FH, "FH". + +The layers are returned in the order an open() or binmode() call would +use them. Note that the "default stack" depends on the operating +system and on the Perl version, and both the compile-time and +runtime configurations of Perl. + +The following table summarizes the default layers on UNIX-like and +DOS-like platforms and depending on the setting of the C<$ENV{PERLIO}>: + + PERLIO UNIX-like DOS-like + ------ --------- -------- + unset / "" unix perlio / stdio [1] unix crlf + stdio unix perlio / stdio [1] stdio + perlio unix perlio unix perlio + mmap unix mmap unix mmap + + # [1] "stdio" if Configure found out how to do "fast stdio" (depends + # on the stdio implementation) and in Perl 5.8, otherwise "unix perlio" + +By default the layers from the input side of the filehandle is +returned, to get the output side use the optional C argument: + + my @layers = PerlIO::get_layers($fh, output => 1); + +(Usually the layers are identical on either side of a filehandle but +for example with sockets there may be differences, or if you have +been using the C pragma.) + +There is no set_layers(), nor does get_layers() return a tied array +mirroring the stack, or anything fancy like that. This is not +accidental or unintentional. The PerlIO layer stack is a bit more +complicated than just a stack (see for example the behaviour of C<:raw>). +You are supposed to use open() and binmode() to manipulate the stack. + +B + +The arguments to layers are by default returned in parenthesis after +the name of the layer, and certain layers (like C) are not real +layers but instead flags on real layers: to get all of these returned +separately use the optional C
argument: + + my @layer_and_args_and_flags = PerlIO::get_layers($fh, details => 1); + +The result will be up to be three times the number of layers: +the first element will be a name, the second element the arguments +(unspecified arguments will be C), the third element the flags, +the fourth element a name again, and so forth. + +B + =head1 AUTHOR Nick Ing-Simmons Enick@ing-simmons.netE =head1 SEE ALSO -L, L, L, L +L, L, L, L, +L =cut -