/usr/man/cat.3/PerlIO.3.Z(/usr/man/cat.3/PerlIO.3.Z)

NAME

       PerlIO - On demand loader for PerlIO layers and root of PerlIO::* name
       space

SYNOPSIS

         open($fh,"<:crlf", "my.txt"); # portably open a text file for reading

         open($fh,"<","his.jpg");      # portably open a binary file for reading
         binmode($fh);

         Shell:
           PERLIO=perlio perl ....

DESCRIPTION

       When an undefined layer 'foo' is encountered in an "open" or "binmode"
       layer specification then C code performs the equivalent of:

         use PerlIO 'foo';

       The perl code in PerlIO.pm then attempts to locate a layer by doing

         require PerlIO::foo;

       Otherwise the "PerlIO" package is a place holder for additional PerlIO
       related functions.

       The following layers are currently defined:

       unix
           Low level layer which calls "read", "write" and "lseek" etc.

       stdio
           Layer which calls "fread", "fwrite" and "fseek"/"ftell" 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.

       perlio
           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.

       crlf
           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 not mimic MS-DOS as far as treating of
           Control-Z as being an end-of-file marker.)

       utf8
           Declares that the stream accepts perl's internal encoding of char-
           acters.  (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 is chosen to render simple text parts (i.e.  non-accented
           letters, digits and common punctuation) human readable in the
           encoded file.

           Here is how to write your native data out using UTF-8 (or
           UTF-EBCDIC) and then read it back in.

                   open(F, ">:utf8", "data.utf");
                   print F $out;
                   close(F);

                   open(F, "<:utf8", "data.utf");
                   $in = <F>;
                   close(F);

       bytes
           This is the inverse of ":utf8" layer. It turns off the flag on the
           layer below so that data read from it is considered to 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.

       raw The ":raw" layer is defined as being identical to calling "bin-
           mode($fh)" - 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 ":raw" is not just the inverse of
           ":crlf" - other layers which would affect the binary nature of the
           stream are also removed or disabled.

           The implementation of ":raw" is as a pseudo-layer which when
           "pushed" pops itself and then any layers which do not declare them-
           selves as suitable for binary data. (Undoing :utf8 and :crlf are
           implemented by clearing flags rather than poping layers but that is
           an implementation detail.)

           As a consequence of the fact that ":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
           a known base on which to build e.g.

               open($fh,":raw:utf8",...)

           will construct a "binary" stream, but then enable UTF-8 transla-
           tion.

       pop A pseudo layer that removes the top-most layer. Gives perl code a
           way to manipulate the layer stack. Should be considered as experi-
           mental. Note that ":pop" only works on real layers and will not
           undo the effects of pseudo layers like ":utf8".  An example of a
           possible use might be:

               open($fh,...)
               ...
               binmode($fh,":encoding(...)");  # next chunk is encoded
               ...
               binmode($fh,":pop");            # back to un-encocded

           A more elegant (and safer) interface is needed.

       Alternatives to raw

       To get a binary stream an alternate method is to use:

           open($fh,"whatever")
           binmode($fh);

       this has advantage of being backward compatible with how such things
       have had to be coded on some platforms for years.

       To get an un-buffered stream specify an unbuffered layer (e.g. ":unix")
       in the open call:

           open($fh,"<:unix",$path)

       Defaults and how to override them

       If the platform is MS-DOS like and normally does CRLF to "\n" transla-
       tion for text files then the default layers are :

         unix crlf

       (The low level "unix" layer may be replaced by a platform specific low
       level layer.)

       Otherwise if "Configure" found out how to do "fast" IO using system's
       stdio, then the default layers are :

         unix stdio

       Otherwise the default layers are

         unix perlio

       These defaults may change once perlio has been better tested and tuned.

       The default can be overridden by setting the environment variable PER-
       LIO to a space separated list of layers (unix 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.

         cd .../perl/t
         PERLIO=stdio  ./perl harness
         PERLIO=perlio ./perl harness

AUTHOR

       Nick Ing-Simmons <nick@ing-simmons.net>

/usr/man/cat.3/PerlIO.3.Z(/usr/man/cat.3/PerlIO.3.Z)

NAME

SYNOPSIS

DESCRIPTION

AUTHOR

SEE ALSO