comment on

Someone on freenode #perl was asking about hooking STDIN, STDOUT, and STDERR to functions so that when things are read or written to those filehandles, they would be pre-processed. I suggested tie(), and then mentioned that an encoding could probably also do the trick.

So I wrote the following snarky little program:

#!/usr/bin/perl

use strict;
use warnings;

{
  package MyEnc;

  use base qw( Encode::Encoding );
  __PACKAGE__->Define(qw( japhy ));

  sub encode {
    my ($self, $str, $chk) = @_;
    $_[1] = '' if $chk;
    $str =~ s/^/> /mg;
    return $str;
  }

  sub decode {
    my ($self, $str, $chk) = @_;
    $_[1] = '' if $chk;
    $str =~ s/^< //mg;
    return $str;
  }
}

open my($in), "<:encoding(japhy)", "input" or die $!;
open my($out), ">:encoding(japhy)", "output" or die $!;
print $out $_ while <$in>;
[download]

If 'input' contains

< abc
< def
[download]

then 'output' ends up holding

> abc
> def
[download]

Proof-of-concept. Hooray. But then I tried using STDIN and STDOUT instead:

open my($in), "<&:encoding(japhy)", "STDIN" or die $!;
open my($out), ">&:encoding(japhy)", "STDOUT" or die $!;
[download]

I entered the same content as is in 'input', but it wasn't decoded, and I got this instead:

< > abc
< > def
[download]

I tried this, too:

open my($in), "<-:encoding(japhy)" or die $!;
open my($out), ">-:encoding(japhy)" or die $!;
[download]

That didn't decode OR encode! I had to call binmode() after opening the filehandles to get it to work.

So, what's the deal? Vitals:

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.15, archname=i486-linux-gnu-thread-multi
    uname='linux ninsei 2.6.15 #1 smp preempt sat jan 7 12:47:52 pst 2
+006 i686 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dccc
+dlflags=-fPIC -Darchname=i486-
linux-gnu -Dprefix=/usr -Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/l
+ib/perl/5.8 -Dvendorprefix=/us
r -Dvendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefi
+x=/usr/local -Dsitelib=/usr/lo
cal/share/perl/5.8.8 -Dsitearch=/usr/local/lib/perl/5.8.8 -Dman1dir=/u
+sr/share/man/man1 -Dman3dir=/u
sr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr
+/local/man/man3 -Dman1ext=1 -D
man3ext=3perl -Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio 
+-Uusenm -Duseshrplib -Dlibperl=
libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define usemulti
+plicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=undef use64bitall=undef uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS 
+-DDEBIAN -fno-strict-aliasing 
-pipe -Wdeclaration-after-statement -I/usr/local/include -D_LARGEFILE_
+SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN 
+-fno-strict-aliasing -pipe
-Wdeclaration-after-statement -I/usr/local/include'
    ccversion='', gccversion='4.0.3 20060128 (prerelease) (Debian 4.0.
+2-8)', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=1
+2
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t',
+ lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.5.so, so=so, useshrplib=true, libperl=libperl.s
+o.5.8.8
    gnulibc_version='2.3.5'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'


Characteristics of this binary (from libperl): 
  Compile-time options: MULTIPLICITY PERL_IMPLICIT_CONTEXT
                        PERL_MALLOC_WRAP THREADS_HAVE_PIDS USE_ITHREAD
+S
                        USE_LARGE_FILES USE_PERLIO USE_REENTRANT_API
  Built under linux
  Compiled at Feb  9 2006 22:12:59
  %ENV:
    PERL5LIB="/home/japhy/perllib/share/perl/5.8.7"
  @INC:
    /home/japhy/perllib/share/perl/5.8.7
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    /usr/local/lib/perl/5.8.7
    /usr/local/share/perl/5.8.7
[download]

Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

In reply to Encodings not latching onto STDIN by japhy

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		`&`
	<		`<`
	>		`>`
	[		`[`
	]		`]`

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.