6 require 5.008001; # for PerlIO::get_layers()
11 return ($1, Encode::resolve_alias($1)) if $_[0] =~ /^:?encoding\((.+)\)$/;
16 require Carp; goto &Carp::croak;
20 # If by the time we arrive here there already is at the top of the
21 # perlio layer stack an encoding identical to what we would like
22 # to push via this open pragma, we will pop away the old encoding
23 # (+utf8) so that we can push ourselves in place (this is easier
24 # than ignoring pushing ourselves because of the way how ${^OPEN}
25 # works). So we are looking for something like
27 # stdio encoding(xxx) utf8
29 # in the existing layer stack, and in the new stack chunk for
33 # If we find a match, we pop the old stack (once, since
34 # the utf8 is just a flag on the encoding layer)
36 return unless @new >= 1 && $new[-1] =~ /^:encoding\(.+\)$/;
37 my @old = PerlIO::get_layers($h);
38 return unless @old >= 3 &&
40 $old[-2] =~ /^encoding\(.+\)$/;
42 my ($loname, $lcname) = _get_encname($old[-2]);
43 unless (defined $lcname) { # Should we trust get_layers()?
44 croak("open: Unknown encoding '$loname'");
46 my ($voname, $vcname) = _get_encname($new[-1]);
47 unless (defined $vcname) {
48 croak("open: Unknown encoding '$voname'");
50 if ($lcname eq $vcname) {
51 binmode($h, ":pop"); # utf8 is part of the encoding layer
56 my ($class,@args) = @_;
57 croak("open: needs explicit list of PerlIO layers") unless @args;
59 my ($in,$out) = split(/\0/,(${^OPEN} || "\0"), -1);
61 my $type = shift(@args);
63 if ($type =~ /^:?(utf8|locale|encoding\(.+\))$/) {
66 } elsif ($type eq ':std') {
70 $dscp = shift(@args) || '';
73 foreach my $layer (split(/\s+/,$dscp)) {
75 if ($layer eq 'locale') {
78 $locale_encoding = encoding::_get_locale_encoding()
79 unless defined $locale_encoding;
80 (warnings::warnif("layer", "Cannot figure out an encoding to use"), last)
81 unless defined $locale_encoding;
82 $layer = "encoding($locale_encoding)";
85 my $target = $layer; # the layer name itself
86 $target =~ s/^(\w+)\(.+\)$/$1/; # strip parameters
88 unless(PerlIO::Layer::->find($target,1)) {
89 warnings::warnif("layer", "Unknown PerlIO layer '$target'");
93 if ($layer =~ /^(crlf|raw)$/) {
94 $^H{"open_$type"} = $layer;
98 _drop_oldenc(*STDIN, @val) if $std;
99 $in = join(' ', @val);
101 elsif ($type eq 'OUT') {
103 _drop_oldenc(*STDOUT, @val);
104 _drop_oldenc(*STDERR, @val);
106 $out = join(' ', @val);
108 elsif ($type eq 'IO') {
110 _drop_oldenc(*STDIN, @val);
111 _drop_oldenc(*STDOUT, @val);
112 _drop_oldenc(*STDERR, @val);
114 $in = $out = join(' ', @val);
117 croak "Unknown PerlIO layer class '$type' (need IN, OUT or IO)";
120 ${^OPEN} = join("\0", $in, $out);
123 if ($in =~ /:utf8\b/) {
124 binmode(STDIN, ":utf8");
125 } elsif ($in =~ /(\w+\(.+\))/) {
126 binmode(STDIN, ":$1");
130 if ($out =~ /:utf8\b/) {
131 binmode(STDOUT, ":utf8");
132 binmode(STDERR, ":utf8");
133 } elsif ($out =~ /(\w+\(.+\))/) {
134 binmode(STDOUT, ":$1");
135 binmode(STDERR, ":$1");
146 open - perl pragma to set default PerlIO layers for input and output
150 use open IN => ':crlf', OUT => ':raw';
151 open my $in, '<', 'foo.txt' or die "open failed: $!";
152 my $line = <$in>; # CRLF translated
154 open my $out, '>', 'bar.txt' or die "open failed: $!";
155 print $out $line; # no translation of bytes
158 use open OUT => ':encoding(UTF-8)';
159 use open IN => ':encoding(iso-8859-7)';
161 use open IO => ':locale';
163 # IO implicit only for :utf8, :encoding, :locale
164 use open ':encoding(UTF-8)';
165 use open ':encoding(iso-8859-7)';
168 # with :std, also affect global standard handles
169 use open ':std', ':encoding(UTF-8)';
170 use open ':std', OUT => ':encoding(cp1252)';
171 use open ':std', IO => ':raw :encoding(UTF-16LE)';
175 Full-fledged support for I/O layers is now implemented provided
176 Perl is configured to use PerlIO as its IO system (which has been the
177 default since 5.8, and the only supported configuration since 5.16).
179 The C<open> pragma serves as one of the interfaces to declare default
180 "layers" (previously known as "disciplines") for all I/O. Any open(),
181 readpipe() (aka qx//) and similar operators found within the
182 lexical scope of this pragma will use the declared defaults via the
183 L<C<${^OPEN}>|perlvar/${^OPEN}> variable.
185 Layers are specified with a leading colon by convention. You can
186 specify a stack of multiple layers as a space-separated string.
187 See L<PerlIO> for more information on the available layers.
189 With the C<IN> subpragma you can declare the default layers
190 of input streams, and with the C<OUT> subpragma you can declare
191 the default layers of output streams. With the C<IO> subpragma
192 (may be omitted for C<:utf8>, C<:locale>, or C<:encoding>) you
193 can control both input and output streams simultaneously.
195 When open() is given an explicit list of layers (with the three-arg
196 syntax), they override the list declared using this pragma. open() can
197 also be given a single colon (:) for a layer name, to override this pragma
198 and use the default as detailed in
199 L<PerlIO/Defaults and how to override them>.
201 To translate from and to an arbitrary text encoding, use the C<:encoding>
202 layer. The matching of encoding names in C<:encoding> is loose: case does
203 not matter, and many encodings have several aliases. See
204 L<Encode::Supported> for details and the list of supported locales.
206 If you want to set your encoding layers based on your
207 locale environment variables, you can use the C<:locale> pseudo-layer.
210 $ENV{LANG} = 'ru_RU.KOI8-R';
211 # the :locale will probe the locale environment variables like LANG
212 use open OUT => ':locale';
213 open(my $out, '>', 'koi8') or die "open failed: $!";
214 print $out chr(0x430); # CYRILLIC SMALL LETTER A = KOI8-R 0xc1
216 open(my $in, '<', 'koi8') or die "open failed: $!";
217 printf "%#x\n", ord(<$in>); # this should print 0xc1
220 The logic of C<:locale> is described in full in
221 L<encoding/The C<:locale> sub-pragma>,
222 but in short it is first trying nl_langinfo(CODESET) and then
223 guessing from the LC_ALL and LANG locale environment variables.
224 C<:locale> also implicitly turns on C<:std>.
226 C<:std> is not a layer but an additional subpragma. When specified in the
227 import list, it activates an additional functionality of pushing the
228 layers selected for input/output handles to the standard filehandles
229 (STDIN, STDOUT, STDERR). If the new layers and existing layer stack both
230 end with an C<:encoding> layer, the existing C<:encoding> layer will also
233 For example, if both input and out are chosen to be C<:encoding(UTF-8)>, a
234 C<:std> will mean that STDIN, STDOUT, and STDERR will also have
235 C<:encoding(UTF-8)> set. On the other hand, if only output is chosen to
236 be in C<:encoding(koi8r)>, a C<:std> will cause only the STDOUT and STDERR
239 The effect of C<:std> is not lexical as it modifies the layer stack of the
240 global handles. If you wish to apply only this global effect and not the
241 effect on handles that are opened in that scope, you can isolate the call
242 to this pragma in its own lexical scope.
244 { use open ':std', IO => ':encoding(UTF-8)' }
246 =head1 IMPLEMENTATION DETAILS
248 There is a class method in C<PerlIO::Layer> C<find> which is
249 implemented as XS code. It is called by C<import> to validate the
252 PerlIO::Layer::->find("perlio")
254 The return value (if defined) is a Perl object, of class
255 C<PerlIO::Layer> which is created by the C code in F<perlio.c>. As
256 yet there is nothing useful you can do with the object at the perl
261 L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>,