| 1 | package PerlIO; |
| 2 | |
| 3 | our $VERSION = '1.01'; |
| 4 | |
| 5 | # Map layer name to package that defines it |
| 6 | our %alias; |
| 7 | |
| 8 | sub import |
| 9 | { |
| 10 | my $class = shift; |
| 11 | while (@_) |
| 12 | { |
| 13 | my $layer = shift; |
| 14 | if (exists $alias{$layer}) |
| 15 | { |
| 16 | $layer = $alias{$layer} |
| 17 | } |
| 18 | else |
| 19 | { |
| 20 | $layer = "${class}::$layer"; |
| 21 | } |
| 22 | eval "require $layer"; |
| 23 | warn $@ if $@; |
| 24 | } |
| 25 | } |
| 26 | |
| 27 | 1; |
| 28 | __END__ |
| 29 | |
| 30 | =head1 NAME |
| 31 | |
| 32 | PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name space |
| 33 | |
| 34 | =head1 SYNOPSIS |
| 35 | |
| 36 | open($fh,">:crlf","my.txt") |
| 37 | open($fh,">:raw","his.jpg") |
| 38 | |
| 39 | Shell: |
| 40 | PERLIO=perlio perl .... |
| 41 | |
| 42 | =head1 DESCRIPTION |
| 43 | |
| 44 | When an undefined layer 'foo' is encountered in an C<open> or |
| 45 | C<binmode> layer specification then C code performs the equivalent of: |
| 46 | |
| 47 | use PerlIO 'foo'; |
| 48 | |
| 49 | The perl code in PerlIO.pm then attempts to locate a layer by doing |
| 50 | |
| 51 | require PerlIO::foo; |
| 52 | |
| 53 | Otherwise the C<PerlIO> package is a place holder for additional |
| 54 | PerlIO related functions. |
| 55 | |
| 56 | The following layers are currently defined: |
| 57 | |
| 58 | =over 4 |
| 59 | |
| 60 | =item unix |
| 61 | |
| 62 | Low level layer which calls C<read>, C<write> and C<lseek> etc. |
| 63 | |
| 64 | =item stdio |
| 65 | |
| 66 | Layer which calls C<fread>, C<fwrite> and C<fseek>/C<ftell> etc. Note |
| 67 | that as this is "real" stdio it will ignore any layers beneath it and |
| 68 | got straight to the operating system via the C library as usual. |
| 69 | |
| 70 | =item perlio |
| 71 | |
| 72 | This is a re-implementation of "stdio-like" buffering written as a |
| 73 | PerlIO "layer". As such it will call whatever layer is below it for |
| 74 | its operations. |
| 75 | |
| 76 | =item crlf |
| 77 | |
| 78 | A layer which does CRLF to "\n" translation distinguishing "text" and |
| 79 | "binary" files in the manner of MS-DOS and similar operating systems. |
| 80 | |
| 81 | =item utf8 |
| 82 | |
| 83 | Declares that the stream accepts perl's internal encoding of |
| 84 | characters. (Which really is UTF-8 on ASCII machines, but is |
| 85 | UTF-EBCDIC on EBCDIC machines.) This allows any character perl can |
| 86 | represent to be read from or written to the stream. The UTF-X encoding |
| 87 | is chosen to render simple text parts (i.e. non-accented letters, |
| 88 | digits and common punctuation) human readable in the encoded file. |
| 89 | |
| 90 | Here is how to write your native data out using UTF-8 (or UTF-EBCDIC) |
| 91 | and then read it back in. |
| 92 | |
| 93 | open(F, ">:utf8", "data.utf"); |
| 94 | print F $out; |
| 95 | close(F); |
| 96 | |
| 97 | open(F, "<:utf8", "data.utf"); |
| 98 | $in = <F>; |
| 99 | close(F); |
| 100 | |
| 101 | =item bytes |
| 102 | |
| 103 | This is the inverse of C<:utf8> layer. It turns off the flag |
| 104 | on the layer below so that data read from it is considered to |
| 105 | be "octets" i.e. characters in range 0..255 only. Likewise |
| 106 | on output perl will warn if a "wide" character is written |
| 107 | to a such a stream. |
| 108 | |
| 109 | =item raw |
| 110 | |
| 111 | A pseudo-layer which performs two functions (which is messy, but |
| 112 | necessary to maintain compatibility with non-PerlIO builds of Perl |
| 113 | and their way things have been documented elsewhere). |
| 114 | |
| 115 | Firstly it forces the file handle to be considered binary at that |
| 116 | point in the layer stack, i.e. it turns off any CRLF translation. |
| 117 | |
| 118 | Secondly in prevents the IO system seaching back before it in the |
| 119 | layer specification. Thus: |
| 120 | |
| 121 | open($fh,":raw:perlio",...) |
| 122 | |
| 123 | Forces the use of C<perlio> layer even if the platform default, or |
| 124 | C<use open> default is something else (such as ":encoding(iso-8859-7)") |
| 125 | (the C<:encoding> requires C<use Encode>) which would interfere with |
| 126 | binary nature of the stream. |
| 127 | |
| 128 | =back |
| 129 | |
| 130 | =head2 Defaults and how to override them |
| 131 | |
| 132 | If the platform is MS-DOS like and normally does CRLF to "\n" |
| 133 | translation for text files then the default layers are : |
| 134 | |
| 135 | unix crlf |
| 136 | |
| 137 | (The low level "unix" layer may be replaced by a platform specific low |
| 138 | level layer.) |
| 139 | |
| 140 | Otherwise if C<Configure> found out how to do "fast" IO using system's |
| 141 | stdio, then the default layers are : |
| 142 | |
| 143 | unix stdio |
| 144 | |
| 145 | Otherwise the default layers are |
| 146 | |
| 147 | unix perlio |
| 148 | |
| 149 | These defaults may change once perlio has been better tested and tuned. |
| 150 | |
| 151 | The default can be overridden by setting the environment variable |
| 152 | PERLIO to a space separated list of layers (unix or platform low level |
| 153 | layer is always pushed first). |
| 154 | |
| 155 | This can be used to see the effect of/bugs in the various layers e.g. |
| 156 | |
| 157 | cd .../perl/t |
| 158 | PERLIO=stdio ./perl harness |
| 159 | PERLIO=perlio ./perl harness |
| 160 | |
| 161 | =head1 AUTHOR |
| 162 | |
| 163 | Nick Ing-Simmons E<lt>nick@ing-simmons.netE<gt> |
| 164 | |
| 165 | =head1 SEE ALSO |
| 166 | |
| 167 | L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<Encode> |
| 168 | |
| 169 | =cut |
| 170 | |