| 1 | package PerlIO; |
| 2 | |
| 3 | # Map layer name to package that defines it |
| 4 | my %alias = (encoding => 'Encode'); |
| 5 | |
| 6 | sub import |
| 7 | { |
| 8 | my $class = shift; |
| 9 | while (@_) |
| 10 | { |
| 11 | my $layer = shift; |
| 12 | if (exists $alias{$layer}) |
| 13 | { |
| 14 | $layer = $alias{$layer} |
| 15 | } |
| 16 | else |
| 17 | { |
| 18 | $layer = "${class}::$layer"; |
| 19 | } |
| 20 | eval "require $layer"; |
| 21 | warn $@ if $@; |
| 22 | } |
| 23 | } |
| 24 | |
| 25 | 1; |
| 26 | __END__ |
| 27 | |
| 28 | =head1 NAME |
| 29 | |
| 30 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
| 31 | |
| 32 | =head1 SYNOPSIS |
| 33 | |
| 34 | open($fh,">:crlf","my.txt") |
| 35 | open($fh,">:raw","his.jpg") |
| 36 | |
| 37 | Shell: |
| 38 | PERLIO=perlio perl .... |
| 39 | |
| 40 | =head1 DESCRIPTION |
| 41 | |
| 42 | When an undefined layer 'foo' is encountered in an C<open> or |
| 43 | C<binmode> layer specification then C code performs the equivalent of: |
| 44 | |
| 45 | use PerlIO 'foo'; |
| 46 | |
| 47 | The perl code in PerlIO.pm then attempts to locate a layer by doing |
| 48 | |
| 49 | require PerlIO::foo; |
| 50 | |
| 51 | Otherwise the C<PerlIO> package is a place holder for additional |
| 52 | PerlIO related functions. |
| 53 | |
| 54 | The following layers are currently defined: |
| 55 | |
| 56 | =over 4 |
| 57 | |
| 58 | =item unix |
| 59 | |
| 60 | Low level layer which calls C<read>, C<write> and C<lseek> etc. |
| 61 | |
| 62 | =item stdio |
| 63 | |
| 64 | Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note |
| 65 | that as this is "real" stdio it will ignore any layers beneath it and |
| 66 | got straight to the operating system via the C library as usual. |
| 67 | |
| 68 | =item perlio |
| 69 | |
| 70 | This is a re-implementation of "stdio-like" buffering written as a |
| 71 | PerlIO "layer". As such it will call whatever layer is below it for |
| 72 | its operations. |
| 73 | |
| 74 | =item crlf |
| 75 | |
| 76 | A layer which does CRLF to "\n" translation distinguishing "text" and |
| 77 | "binary" files in the manner of MS-DOS and similar operating systems. |
| 78 | |
| 79 | =item utf8 |
| 80 | |
| 81 | Declares that the stream accepts perl's internal encoding of |
| 82 | characters. (Which really is UTF-8 on ASCII machines, but is |
| 83 | UTF-EBCDIC on EBCDIC machines.) This allows any character perl can |
| 84 | represent to be read from or written to the stream. The UTF-X encoding |
| 85 | is chosen to render simple text parts (i.e. non-accented letters, |
| 86 | digits and common punctuation) human readable in the encoded file. |
| 87 | |
| 88 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
| 89 | and then read it back in. |
| 90 | |
| 91 | open(F, ">:utf8", "data.utf"); |
| 92 | print F $out; |
| 93 | close(F); |
| 94 | |
| 95 | open(F, "<:utf8", "data.utf"); |
| 96 | $in = <F>; |
| 97 | close(F); |
| 98 | |
| 99 | =item raw |
| 100 | |
| 101 | A pseudo-layer which performs two functions (which is messy, but |
| 102 | necessary to maintain compatibility with non-PerlIO builds of Perl |
| 103 | and their way things have been documented elsewhere). |
| 104 | |
| 105 | Firstly it forces the file handle to be considered binary at that |
| 106 | point in the layer stack, |
| 107 | |
| 108 | Secondly in prevents the IO system seaching back before it in the |
| 109 | layer specification. Thus: |
| 110 | |
| 111 | open($fh,":raw:perlio",...) |
| 112 | |
| 113 | Forces the use of C<perlio> layer even if the platform default, or |
| 114 | C<use open> default is something else (such as ":encoding(iso-8859-7)") |
| 115 | (the C<:encoding> requires C<use Encode>) which would interfere with |
| 116 | binary nature of the stream. |
| 117 | |
| 118 | =back |
| 119 | |
| 120 | =head2 Defaults and how to override them |
| 121 | |
| 122 | If the platform is MS-DOS like and normally does CRLF to "\n" |
| 123 | translation for text files then the default layers are : |
| 124 | |
| 125 | unix crlf |
| 126 | |
| 127 | (The low level "unix" layer may be replaced by a platform specific low |
| 128 | level layer.) |
| 129 | |
| 130 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
| 131 | stdio, then the default layers are : |
| 132 | |
| 133 | unix stdio |
| 134 | |
| 135 | Otherwise the default layers are |
| 136 | |
| 137 | unix perlio |
| 138 | |
| 139 | These defaults may change once perlio has been better tested and tuned. |
| 140 | |
| 141 | The default can be overridden by setting the environment variable |
| 142 | PERLIO to a space separated list of layers (unix or platform low level |
| 143 | layer is always pushed first). |
| 144 | |
| 145 | This can be used to see the effect of/bugs in the various layers e.g. |
| 146 | |
| 147 | cd .../perl/t |
| 148 | PERLIO=stdio ./perl harness |
| 149 | PERLIO=perlio ./perl harness |
| 150 | |
| 151 | =head1 AUTHOR |
| 152 | |
| 153 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
| 154 | |
| 155 | =head1 SEE ALSO |
| 156 | |
| 157 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
| 158 | |
| 159 | =cut |
| 160 | |