Updated 2013-01-18 16:00:50 by pooryorick

Richard Suchenwirth 2007-02-15 - A colleague wanted a way to capture stdout of a Tcl process temporarily redirected into a variable. Here's my solution, another puts workaround done by briefly overloading puts, and restoring it afterwards:
proc getputs body {
    variable putsbuffer ""
    if {[info commands puts_] eq ""} {
        rename puts puts_
    proc puts args {
        set str   [lindex $args end]
        set arg1  [lindex $args 0]
        set nonew [string equal $arg1 -nonewline]
        switch -glob [llength $args],$nonew  {
            1,* {set chan stdout; append str \n}
            2,0 {set chan $arg1;  append str \n}
            2,1 {set chan stdout}
            3,1 {set chan [lindex $args 1]}
            default {
                error {wrong \# args: should be "puts ?-nonewline? ?channelId? string"}
       if {$chan ne "stdout"} {
           puts_ -nonewline $chan $str
       } else {append ::putsbuffer $str}
    set code [catch {uplevel 1 $body} res]
    if {$code} {append putsbuffer $code:$res}
    rename puts  {}
    rename puts_ puts
    return -code $code $putsbuffer

#--- Testing:

puts before
set var [getputs {
    puts -nonewline hello,
    puts world
    puts stdout inside!
    puts stderr stderr...
    #expr 1/0

puts after:[string toupper $var]

which shows on stdout: