I'm making a function that can read the metadata of the current song playing in spotify. This is being programmed in lua since it is an implementation for awesome wm. I got the following line to get all the metadata that I can later use.
handle = io.popen('qdbus org.mpris.MediaPlayer2.spotify /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.Metadata | awk -F: \'{$1=\"\";$2=\"\";print substr($0,4)}\'')
However when Spotify is not running I don't get the expected information and qdbus writes an error to the stderr stream. I wanted to use the fact that qdbus writes to the error stream to determine a fault and stop the program there. (This should also catch any other errors not related to wheter spotify is running or not)
My understanding is that lua popen uses popen3 that can subdivide between stdout and stderr. but all my efforts so far are fruitless and my error stream is always empty. Is it possible to check for a non nil value in the stderr in order to determine a faulty call to qdbus (or awk)?
thanks!
I think you can redirect stderr to stdout in the call to popen like this:
handle = io.popen("somecommand 2>&1")
If you want to differentiate stderr and stdout, you cannot do it with the io library but you can with luaposix. See this answer for instance.
You can checkout juci.exec which I wrote for JUCI webgui. I struggled with the same problem and I ended up using luaposix for this kind of thing when I really need two separate streams. My implementation also gives you the program exit code which is good for testing for errors: https://github.com/mkschreder/juci/blob/master/juci/lua/core.lua
Related
I am writing a small program in Progress that needs to write an error message to the system's standard error. What ways, simple if at all possible, can I use to print to standard error?
I am using OpenEdge 11.3.
When on Windows (10.2B+) you can use .NET:
System.Console:Error:WriteLine ("This is an error message") .
together with
prowin32 2> stderr.out
Progress doesn't provide a way to write to stderr - the easiest way I can think of is to output-through an external program that takes stdin and echoes it to stderr.
You could look into LOG-MANAGER:WRITE-MESSAGE. It won't log to standard output or standard error, but to a client-specific log. This log should be monitored in any case (specifically if the client is an application server).
From the documentation:
For an interactive or batch client, the WRITE-MESSAGE( ) method writes the log entries to the log file specified by the LOGFILE-NAME attribute or the Client Logging (-clientlog) startup parameter. For WebSpeed agents and AppServer servers, the WRITE-MESSAGE() method writes the log entries to the server log file. For DataServers, the WRITE-MESSAGE() method writes the log entries to the log file specified by the DataServer Logging (-dslog) startup parameter.
LOG-MANAGER:WRITE-MESSAGE("Got here, x=" + STRING(x), "DEBUG1").
Will write this in the log:
[04/12/05#13:19:19.742-0500] P-003616 T-001984 1 4GL DEBUG1 Got here, x=5
There are quite a lot of options regarding the LOG-MANAGER system, what messages to display, where the file is placed, etc.
There is no easy way, but in Unixen you can always do something like this using OUTPUT THROUGH (untested):
output through "cat >&2" no-echo unbuffered.
Alternatively -- and this is tested -- if you just want error messages from a batch-mode program to go to standard out then
output through "tee" ...
...definitely works.
I am using Verilator to incorporate an algorithm written in SystemVerilog into an executable utility that manipulates I/O streams passed via stdin and stdout. Unfortunately, when I use the SystemVerilog $display() function, the output goes to stdout. I would like it to go to stderr so that stdout remains uncontaminated for my other purposes.
How can I make this happen?
Thanks to #toolic for pointing out the existence of $fdisplay(), which can be used thusly...
$fdisplay(STDERR,"hello world"); // also supports formatted arguments
IEEE Std 1800-2012 states that STDERR should be pre-opened, but it did not seem to be known to Verilator. A workaround for this is:
integer STDERR = 32'h8000_0002;
Alternatively, you can create a log file handle for use with $fdisplay() like so...
integer logfile;
initial begin
$system("echo 'initial at ['$(date)']'>>temp.log");
logfile = $fopen("temp.log","a"); // or open with "w" to start fresh
end
It might be nice if you could create a custom wrapper that works like $display but uses your selected file descriptor (without specifying it every time). Unfortunately, that doesn't seem to be possible within the language itself -- but maybe you can do it with the DPI, see DPI Display Functions (I haven't gotten this to work so far).
I want read on stdout to be non-blocking. I was using the newlib-lpc library in WINarm to do this. But even though it is set as non-Blocking, the code stops at read every time and waits for a character to be received.
Here is my read line:
read(fileno(stdout), &inchar, 1);
Here is the code to set stdout to non-blocking using newlib-lpc
blocking=BLOCKING_IO_NO;
ioctl( fileno(stdout), BLOCKING_SETUP, &blocking);
When that didn't work, I decided to forget using the library and do it myself with this line
fcntl(fileno(stdout), F_SETFL,fcntl(fileno(stdout), F_GETFL) |O_NONBLOCK);
But that didn't work either.
Could anyone give me some advice?
Thanks!
edit:
Someone asked if I really meant stdout. Yes, I am resurrecting some old code, and the stdout has been set as the socket for UART communication between my board and the computer.
sp.baud = 115200uL;
sp.length = UART_WORD_LEN_8;
sp.parity = UART_PARITY_NONE;
sp.stop = UART_STOP_BITS_1;
ioctl( fileno(stdout), UART_SETUP, &sp);
irq.FIQ = 0;
irq.pri = (INT_PRIORITY)10;
ioctl( fileno(stdout), INTERRUPT_SETUP, &irq);
edit2: They used stdout this way so that printf works. When it tries to print to stdout, it gets redirected to the UART serial stream.
edit3: The error I get when calling
ioctl( fileno(stdout), BLOCKING_SETUP, &blocking);
is
errno88 function not implemented
Although I am quite familiar with Tcl this is a beginner question. I would like to read and write from a pipe. I would like a solution in pure Tcl and not use a library like Expect. I copied an example from the tcl wiki but could not get it running.
My code is:
cd /tmp
catch {
console show
update
}
proc go {} {
puts "executing go"
set pipe [open "|cat" RDWR]
fconfigure $pipe -buffering line -blocking 0
fileevent $pipe readable [list piperead $pipe]
if {![eof $pipe]} {
puts $pipe "hello cat program!"
flush $pipe
set got [gets $pipe]
puts "result: $got"
}
}
go
The output is executing go\n result:, however I would expect that reading a value from the pipe would return the line that I have sent to the cat program.
What is my error?
--
EDIT:
I followed potrzebie's answer and got a small example working. That's enough to get me going. A quick workaround to test my setup was the following code (not a real solution but a quick fix for the moment).
cd /home/stephan/tmp
catch {
console show
update
}
puts "starting pipe"
set pipe [open "|cat" RDWR]
fconfigure $pipe -buffering line -blocking 0
after 10
puts $pipe "hello cat!"
flush $pipe
set got [gets $pipe]
puts "got from pipe: $got"
Writing to the pipe and flushing won't make the OS multitasking immediately leave your program and switch to the cat program. Try putting after 1000 between the puts and the gets command, and you'll see that you'll probably get the string back. cat has then been given some time slices and has had the chance to read it's input and write it's output.
You can't control when cat reads your input and writes it back, so you'll have to either use fileevent and enter the event loop to wait (or periodically call update), or periodically try reading from the stream. Or you can keep it in blocking mode, in which case gets will do the waiting for you. It will block until there's a line to read, but meanwhile no other events will be responded to. A GUI for example, will stop responding.
The example seem to be for Tk and meant to be run by wish, which enters the event loop automatically at the end of the script. Add the piperead procedure and either run the script with wish or add a vwait command to the end of the script and run it with tclsh.
PS: For line-buffered I/O to work for a pipe, both programs involved have to use it (or no buffering). Many programs (grep, sed, etc) use full buffering when they're not connected to a terminal. One way to prevent them to, is with the unbuffer program, which is part of Expect (you don't have to write an Expect script, it's a stand-alone program that just happens to be included with the Expect package).
set pipe [open "|[list unbuffer grep .]" {RDWR}]
I guess you're executing the code from http://wiki.tcl.tk/3846, the page entitled "Pipe vs Expect". You seem to have omitted the definition of the piperead proc, indeed, when I copy-and-pasted the code from your question, I got an error invalid command name "piperead". If you copy-and-paste the definition from the wiki, you should find that the code works. It certainly did for me.
I wrote the following two functions, and call the second ("callAndWait") from JavaScript running inside Windows Script Host. My overall intent is to call one command line program from another. That is, I'm running the initial scripting using cscript, and then trying to run something else (Ant) from that script.
function readAllFromAny(oExec)
{
if (!oExec.StdOut.AtEndOfStream)
return oExec.StdOut.ReadLine();
if (!oExec.StdErr.AtEndOfStream)
return "STDERR: " + oExec.StdErr.ReadLine();
return -1;
}
// Execute a command line function....
function callAndWait(execStr) {
var oExec = WshShell.Exec(execStr);
while (oExec.Status == 0)
{
WScript.Sleep(100);
var output;
while ( (output = readAllFromAny(oExec)) != -1) {
WScript.StdOut.WriteLine(output);
}
}
}
Unfortunately, when I run my program, I don't get immediate feedback about what the called program is doing. Instead, the output seems to come in fits and starts, sometimes waiting until the original program has finished, and sometimes it appears to have deadlocked. What I really want to do is have the spawned process actually share the same StdOut as the calling process, but I don't see a way to do that. Just setting oExec.StdOut = WScript.StdOut doesn't work.
Is there an alternate way to spawn processes that will share the StdOut & StdErr of the launching process? I tried using "WshShell.Run(), but that gives me a "permission denied" error. That's problematic, because I don't want to have to tell my clients to change how their Windows environment is configured just to run my program.
What can I do?
You cannot read from StdErr and StdOut in the script engine in this way, as there is no non-blocking IO as Code Master Bob says. If the called process fills up the buffer (about 4KB) on StdErr while you are attempting to read from StdOut, or vice-versa, then you will deadlock/hang. You will starve while waiting for StdOut and it will block waiting for you to read from StdErr.
The practical solution is to redirect StdErr to StdOut like this:
sCommandLine = """c:\Path\To\prog.exe"" Argument1 argument2"
Dim oExec
Set oExec = WshShell.Exec("CMD /S /C "" " & sCommandLine & " 2>&1 """)
In other words, what gets passed to CreateProcess is this:
CMD /S /C " "c:\Path\To\prog.exe" Argument1 argument2 2>&1 "
This invokes CMD.EXE, which interprets the command line. /S /C invokes a special parsing rule so that the first and last quote are stripped off, and the remainder used as-is and executed by CMD.EXE. So CMD.EXE executes this:
"c:\Path\To\prog.exe" Argument1 argument2 2>&1
The incantation 2>&1 redirects prog.exe's StdErr to StdOut. CMD.EXE will propagate the exit code.
You can now succeed by reading from StdOut and ignoring StdErr.
The downside is that the StdErr and StdOut output get mixed together. As long as they are recognisable you can probably work with this.
Another technique which might help in this situation is to redirect the standard error stream of the command to accompany the standard output.
Do this by adding "%comspec% /c" to the front and "2>&1" to the end of the execStr string.
That is, change the command you run from:
zzz
to:
%comspec% /c zzz 2>&1
The "2>&1" is a redirect instruction which causes the StdErr output (file descriptor 2) to be written to the StdOut stream (file descriptor 1).
You need to include the "%comspec% /c" part because it is the command interpreter which understands about the command line redirect. See http://technet.microsoft.com/en-us/library/ee156605.aspx
Using "%comspec%" instead of "cmd" gives portability to a wider range of Windows versions.
If your command contains quoted string arguments, it may be tricky to get them right:
the specification for how cmd handles quotes after "/c" seems to be incomplete.
With this, your script needs only to read the StdOut stream, and will receive both standard output and standard error.
I used this with "net stop wuauserv", which writes to StdOut on success (if the service is running)
and StdErr on failure (if the service is already stopped).
First, your loop is broken in that it always tries to read from oExec.StdOut first. If there is no actual output then it will hang until there is. You wont see any StdErr output until StdOut.atEndOfStream becomes true (probably when the child terminates). Unfortunately, there is no concept of non-blocking I/O in the script engine. That means calling read and having it return immediately if there is no data in the buffer. Thus there is probably no way to get this loop to work as you want. Second, WShell.Run does not provide any properties or methods to access the standard I/O of the child process. It creates the child in a separate window, totally isolated from the parent except for the return code. However, if all you want is to be able to SEE the output from the child then this might be acceptable. You will also be able to interact with the child (input) but only through the new window (see SendKeys).
As for using ReadAll(), this would be even worse since it collects all the input from the stream before returning so you wouldn't see anything at all until the stream was closed. I have no idea why the example places the ReadAll in a loop which builds a string, a single if (!WScript.StdIn.AtEndOfStream) should be sufficient to avoid exceptions.
Another alternative might be to use the process creation methods in WMI. How standard I/O is handled is not clear and there doesn't appear to be any way to allocate specific streams as StdIn/Out/Err. The only hope would be that the child would inherit these from the parent but that's what you want, isn't it? (This comment based upon an idea and a little bit of research but no actual testing.)
Basically, the scripting system is not designed for complicated interprocess communication/synchronisation.
Note: Tests confirming the above were performed on Windows XP Sp2 using Script version 5.6. Reference to current (5.8) manuals suggests no change.
Yes, the Exec function seems to be broken when it comes to terminal output.
I have been using a similar function function ConsumeStd(e) {WScript.StdOut.Write(e.StdOut.ReadAll());WScript.StdErr.Write(e.StdErr.ReadAll());} that I call in a loop similar to yours. Not sure if checking for EOF and reading line by line is better or worse.
You might have hit the deadlock issue described on this Microsoft Support site.
One suggestion is to always read both from stdout and stderr.
You could change readAllFromAny to:
function readAllFromAny(oExec)
{
var output = "";
if (!oExec.StdOut.AtEndOfStream)
output = output + oExec.StdOut.ReadLine();
if (!oExec.StdErr.AtEndOfStream)
output = output + "STDERR: " + oExec.StdErr.ReadLine();
return output ? output : -1;
}