TIP: 202
Title: Add 2>@1 Special Case to [open] and [exec]
Version: $Revision: 1.4 $
Author: Jeff Hobbs <[email protected]>
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.