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Full Discussion: what does this code mean?
Top Forums Shell Programming and Scripting what does this code mean? Post 302329380 by drl on Friday 26th of June 2009 10:58:56 PM
Old 06-26-2009
Hi.
Quote:
Originally Posted by new2learn09
I want to know what the "echo 1>&2" means ...
When a program runs, 3 files are made available: STDIN (0), STDOUT (1), and STDERR (2), all assigned to the terminal.

Often programs are connected together into pipelines, where the STDOUT of a program is connected to the STDIN of another program. If a program were to write an error message to STDOUT, it could be swallowed down the pipeline. Consequently,a good practice is to specify that error messages be written to STDERR.

If we were to write :
Code:
echo " Error!" >2

the message would be written on file "2". So the shell uses the convention that "&2" will be whatever STDERR is assigned to. So we write:
Code:
echo " Error!" >&2

Because STDERR is normally assigned to the terminal, the user is likely to notice it. (The "1" in "1>&2" is understood, and may be omitted.)

The placement of "1>&2" can be anywhere where it is directly exposed to the shell:
Code:
>&2 echo One
echo >&2 Two
echo Three >&2

but I have seen it in most situations at the end of the statement.

Best wishes ... cheers, drl
 

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Appender::Screen(3)					User Contributed Perl Documentation				       Appender::Screen(3)

NAME
Log::Log4perl::Appender::Screen - Log to STDOUT/STDERR SYNOPSIS
use Log::Log4perl::Appender::Screen; my $app = Log::Log4perl::Appender::Screen->new( stderr => 0, utf8 => 1, ); $file->log(message => "Log me "); DESCRIPTION
This is a simple appender for writing to STDOUT or STDERR. The constructor "new()" take an optional parameter "stderr", if set to a true value, the appender will log to STDERR. The default setting for "stderr" is 1, so messages will be logged to STDERR by default. If "stderr" is set to a false value, it will log to STDOUT (or, more accurately, whichever file handle is selected via "select()", STDOUT by default). Design and implementation of this module has been greatly inspired by Dave Rolsky's "Log::Dispatch" appender framework. To enable printing wide utf8 characters, set the utf8 option to a true value: my $app = Log::Log4perl::Appender::Screen->new( stderr => 1, utf8 => 1, ); This will issue the necessary binmode command to the selected output channel (stderr/stdout). COPYRIGHT AND LICENSE
Copyright 2002-2009 by Mike Schilli <m@perlmeister.com> and Kevin Goess <cpan@goess.org>. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.12.1 2010-02-07 Appender::Screen(3)
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