Question

I’m looking for some Tcl code that would duplicate what puts command sends to stdout to some log file. Yes, there is a possibility to change all calls to puts to some custom function. But I would like to make it as transparent as possible.
I have this trial code, but it doesn’t really work that well:

set pass_log_output "0"

rename puts _puts
proc puts { args } {
    global pass_log_output

    if {[info exists pass_log_output]} {
        # There can be several cases:
        # -nonewline parameter, stdout specified or not
        set stdout_dest [ lsearch $args stdout ]
        set nonewline [ lsearch $args -nonewline ]
        if { $stdout_dest != -1 } {
            log_low_level "" [lindex $args [expr $stdout_dest + 1]] ""
        } elseif { $nonewline != -1 && [ llength $args ] > 1} {
            log_low_level "" [lindex $args [expr $nonewline + 1]] ""
        } else {
            log_low_level "" [lindex $args 0] ""
        }
    }

    if { [ catch { eval _puts $args } err ] } {
        return -code error $err
    }
}

log_low_level function just stores the passed string in a file.
So far I’m getting this error:

Tcl Interpreter Error: too many nested evaluations (infinite loop?)

Answer 1

Does log_low_level use puts? That could be your infinite loop.

If so, try changing it to use _puts.