DN482531387

Subject: Re: opening two pipes for exec? - DN [1]

"George A. Howlett" <gah@cadence.com> - 27 May 1999 - comp.lang.tcl

 Mark G. Saye <markgsaye@earthlink.net> wrote:

 : I want to exec a command and put the output into a text widget. I'm
 : using the command:

 : set pipe [open "|$command |& cat" r+]
 : fconfigure $pipe -buffering line

 : which returns both stdout and stderr from $command. Can I open a second
 : pipe (to stderr) so that I can add stderr messages into my text widget
 : with a red tag, for instance ? Or is there some other way I can
 : differentiate the two channels when I read from the pipe ? I'd like to
 : be able to read from both pipes simultaneously (i.e. not wait until
 : $command has finished to get stderr)

 : I found a message on Deja saying this could possibly be done with tclX
 : 'pipe' command, but I'm using tcl/tk 8.0.5 (on Linux RH 5.2). Any
 : suggestions would be very helpful.

 The "bgexec" command in BLT lets you do this in a simple,
 straight-forward way.

     text .text
     .text tag configure stdoutTag -foreground green
     .text tag configure stderrTag -foreground red

     proc DisplayOutput { string } {
         .text insert end $string stdoutTag
     }
     proc DisplayErrors { string } {
         .text insert end $string stderrTag
     }

     bgexec myVar \
     -onoutput DisplayOutput -onerror DisplayErrors \
     $command &

 The -onoutput and -onerror switches specify procedures that get called
 whenever data is available on that channel.  Both procedures take one
 argument that is the new data.

 The varible "myVar" gets set when the command is done executing.  It
 will contain the return code, message, etal. of the command.  So you
 can get the command run in the background (using "&" as the last
 argument of the command) and still know when it finishes by putting a
 trace on that variable.

 If you need to stop the command while its running, just set the
 "myVar" and the program will be killed. "bgexec" accepts all the same
 syntax as the "exec" command.  And it works the same way under both
 Unix and Windows.

 --gah