TIP:		202
Title:		Add 2>@1 Special Case to [open] and [exec]
Version:	$Revision: 1.4 $
Author:		Jeff Hobbs <jeffh@activestate.com>
State:		Final
Type:		Project
Tcl-Version:	8.5
Vote:		Done
Created:	19-May-2004
Post-History:	
Keywords:	Tcl, redirection

~ Abstract

This TIP proposes adding a new redirection case '2>@1' that redirects
the error channel to the output channel in '''open''' and '''exec'''.
This would only be valid at the end of a pipeline.

~ Rationale

Tcl is currently limited on how ''stderr'' can be managed from a
command opened with '''open |''' or '''exec'''.  This TIP adds the
ability to simply combine the ''stderr'' stream with the ''stdout''
stream by adding a new output redirection case, '''2>@1''' (i.e. as in
Bourne shell syntax), that is only ever valid as the last redirection
item in a pipeline.  This will enable simple capturing of ''stderr''
as well as ''stdout'' across platforms.

The behavior is similar to '''2>@stdout''', but that does not work
across platforms.  The difference is that directs to a real ''stdout''
file channel (which is not available in Windows wish for example),
whereas '''2>@1''' would redirect to the output result for
'''exec'''/'''open'''.

The intention is to handle the common case of wanting to capture
''stderr'' as well as ''stdout'' output from a single command.  This
operator is only valid as the last redirection operator.  To redirect
''stderr'' of previous commands along with their ''stdout'', use the
preexisting '''|&''' pipe operator.

This is backwards compatible as '''2>@1''' currently raises an error
that "1" is not a valid file id (Tcl does not create such file ids).

~~ Examples

| set fid [open "|$cmd 2>@1"]
| set result [exec $cmd 2>@1]

~ Reference Implementation 

See SF Tcl Patch 957132
[http://sf.net/tracker/?func=detail&aid=957132&group_id=10894&atid=310894]
for details.

~ Copyright 

This document has been placed in the public domain.
