CODEWITHSUNDEEP
tcl
user1476056
user1476056

Reputation: 257

example code to make puts log the output

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?)

Upvotes: 1

Views: 1005

Answers (3)

user1476056
user1476056

Reputation: 257

Thanks for the points. I just want to post the final working code for reference. It even takes care of the storing lines with -nonewline flag properly.

set pass_log_output "0"
set last_call_nonewline 0

rename puts _orig_puts
proc puts { args } {
    global pass_log_output
    global g_log_file
    global last_call_nonewline

    if {[info exists pass_log_output]} {
        # Check if the logging was initialized
        if {![info exists g_log_file]} {
            _orig_puts "Log file wasn't initialized!"
            return
        }

        # There can be several cases:
        # -nonewline parameter, stdout specified or not
        set stdout_dest [ lsearch $args stdout ]
        set nonewline [ lsearch $args -nonewline ]
        if {[ llength $args ] > 3} {
            return -code error "wrong # args: should be puts ?-nonewline? ?channelId? string"
        } elseif { $stdout_dest != -1 } {
            set message [lindex $args end]
        } elseif { $nonewline != -1 && [ llength $args ] == 2} {
            set message [lindex $args [expr $nonewline + 1]]
        } elseif {[ llength $args ] == 1} {
            set message [lindex $args 0]
        }

        # Store the message in the file, if needed.
        # Take into account if the last call was with -nonewline
        if {[info exists message]} {
            if {$last_call_nonewline == 0} {
                _orig_puts -nonewline $g_log_file [clock format [clock seconds] -format "%T - "]
            }
            if {$nonewline != -1} {
                set last_call_nonewline 1
                _orig_puts -nonewline $g_log_file "$message"
            } else {
                set last_call_nonewline 0
                _orig_puts $g_log_file "$message"
            }
            flush $g_log_file
        }
    }

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

Upvotes: 2

glenn jackman
glenn jackman

Reputation: 246764

Since puts has very few options, it may be easier to consider the number of args given. Also, you should contain all uses of the original _puts to your new puts proc -- this new puts should be transparent even to your code.

I assume you only want to log stuff you're writing to stdout

rename puts _orig_puts
proc puts {args} {
    switch -exact [llength $args] {
        3 {
            # both -newline and a channelId are given
            set do_log [expr {[lindex $args 1] eq "stdout"}]
        }
        2 {
            # only log if not writing to stdout
            set chan [lindex $args 0]
            set do_log [expr {$chan eq "-nonewline" || $chan eq "stdout"}]
        }
        1 {
            set do_log true
        }
        default {
            error {wrong # args: should be "puts ?-nonewline? ?channelId? string"}
        }
    }
    if {$do_log} {
        set chan [open $::mylogfile a]
        _orig_puts $chan [lindex $args end]
        close $chan
    } 
    _orig_puts {*}$args
}

Upvotes: 1

Ergwun
Ergwun

Reputation: 12978

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

If so, try changing it to use _puts.

Upvotes: 3

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