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It doesn’t exist before running the program. It is created by the command. If you want to read it, you should open it after the command has finished.
Mircea
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Kindly allow me to "write review".
The OP question was answered.
by placing the redirection as last option of the system call.
Ir was verified by passing by complier / linker and function
returning success ( 0 ).
However, as coded there is no "passed to " function seen in debugger,
( since it is part of the options ?)
and
there is no practical value of the "passed to " function if it cannot be read.
hence there is an extension to my OP
how to read the contents of the "passed to" function ?
after that question extension is answered there will be another
modification
how to "pipe" ca;; result to the console and redirect it to a file SAME time ?
I sincerely appreciate your contribution to resolve this.
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I'm not sure I understand your question. Something might be "lost in translation".
You cannot send results to file and console "at the same time". What you can do is send them to the console right after you sent them to the file. For instance:
ps -A >results && cat results
If what you want is to read the results in your program and process them somehow, you could do something like:
#include <stdlib.h>
#include <stdio.h>
int main ()
{
int ret;
char line[256];
ret = system ("echo xxxxxx | sudo -S ps -A >results");
FILE *f = fopen("results", "r");
while (!feof(f)) {
fgets (line, sizeof(line), f);
puts(line);
}
fclose(f);
return 0;
} I didn't compile this code but should be rather OK.
If you explain better what you want to do maybe I can answer more to the point.
Mircea
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Mircea Neacsu wrote: You cannot send results to file and console "at the same time"
At the risk of further confusing the OP, I'd like to remind you of the tee command
$ ls | tee /tmp/foo
PID TTY TIME CMD
3995778 pts/1 00:00:00 bash
3995865 pts/1 00:00:00 ps
3995866 pts/1 00:00:00 tee
$ cat /tmp/foo
PID TTY TIME CMD
3995778 pts/1 00:00:00 bash
3995865 pts/1 00:00:00 ps
3995866 pts/1 00:00:00 tee
But to the OP's issue, I'd like to, once again, point out that system() is not an ideal tool to use if you want to capture command output. A better option would be to use popen() or a QProcess object. The masochists could also write their own process object that allows reading and writing to the child process, but that's an adventure not for the faint of heart.
"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown
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k5054 wrote: I'd like to remind you of the tee command
True! I forgot about good old tee  Too much time spent in Windowsland
Mircea
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I believe it is time to say that the problem has been solved.
I now have enough info to figure out why
hcitool info 98:D3:31:F8:39:33 takes almost 20 seconds to "complete", however , it goes from immediate " connect " to "disconnect" in few seconds...
(hcitool problem outside CodeProject scope )
In retrospect I would like to point out that I am still not sure how
echo q | sudo -S hcitool cc --role=c 98:D3:31:F8:29:33
works
how do I get "user" in console , but not "password"?
There was two reasons why I shy away from QProcess
I am being chastised every time I ask Qt question, but it is OK to keep showing QProcess to me
especialy when I do not know what is "program" in
echo q | sudo -S hcitool cc --role=c 98:D3:31:F8:29:33
command.
(obviously Qt question )
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Salvatore Terress wrote: obviously Qt question
No, nothing to do with Qt. But then that is (the main) part of your problem, you seem to be confused between what is Qt, the language library or the Linux shell.
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UPDATE ( just to share )
here is working as expected C++ code
system(" echo q | sudo -S hcitool cc --role=c 98:D3:31:F8:29:33");
and here is the result:
[sudo] password for nov25-1: Can't create connection: Input/output error
what is interesting "echo" hides the passed password
the challenge - how to hide [sudo] password for nov25-1:
modified 17-Feb-24 12:05pm.
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Googling provides answers
C++ "sudo" provide password
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Try using a Here Document :
[k5054@localhost]$ sudo ps
[sudo] password for k5054:
sudo: no password was provided
sudo: a password is required
[k5054@localhost]$ cat example.cpp
int main()
{
std::string userPass{"myPassword"};
std::string command{"sudo -S ps -lf 2>/dev/null <<_EOF\n" + userPass + "\n_EOF"};
FILE *pipe = popen(command.c_str(), "r");
char *line = NULL;
size_t len = 0;
ssize_t rlen;
while( (rlen = getline(&line, &len, pipe)) > 0) {
line[--rlen] = '\0'; // trim trailing newline
std::cout << line << '\n';
}
pclose(pipe);
free(line);
}
[k5054@localhost]$ make example
g++ -Wall -Wextra -ggdb example.cpp -o example
[k5054@localhost]$ ./example
F S UID PID PPID C PRI NI ADDR SZ WCHAN STIME TTY TIME CMD
1 S root 4030 4029 0 80 0 - 4799 do_pol 11:49 pts/2 00:00:00 sudo -S ps -lf
4 R root 4031 4030 0 80 0 - 3502 - 11:49 pts/2 00:00:00 ps -lf
[k5054@localhost]$ You should be able to modify that for use with QProcess.
Note that if you don't redirect stderr to /dev/null, the SSH password prompt goes to wherever stderr is pointing to.
"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown
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Thanks,
as I suspected "stdin" and file "pipe" are what I failed to put into THE equation.
Unfortunately all these " well meaning " but superficial, distracting from subject , AKA not answering questions , commentaries about security did not help...
SOLVED
10-4
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Hello folks, just a quick question about the Visual Studio Resource Editor:
Is it possible to use it to edit resources in a compiled executable without the source code? (Specifically the VERSION resource)
I doubt it, but I just wanted to be sure.
The difficult we do right away...
...the impossible takes slightly longer.
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Yes, in the "File Open..." (Ctrl+O) dialog select file type EXE. Select the Version resource, edit it and save the file.
Mircea
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Thanks! I never noticed that capability.
The difficult we do right away...
...the impossible takes slightly longer.
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If the exe (or dll) is signed I am guessing that would not work?
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You still can edit it but it invalidates the signature - makes sense. Never tried it before, thanks for uncovering another detail.
Mircea
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Voluntarily removed- violates "Posting guidelines "
modified 16-Feb-24 12:53pm.
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process->start("sh", QStringList() << "-c" << "xterm");
It looks like you are starting a terminal session via the shell. At a guess the xterm process is running and the shell process that started it is waiting for it to finish. And your application will be waiting until both xterm and its parent shell terminate. At which time I doubt that there will be any stdout to capture.
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Launching a gnome terminal from QT seems like a bit of a frankenstein. Surely a better option would be a terminal widget. A quick google search seems to indicate that QT does not provide a terminal widget, but others have written them, such as this one here. Failing that, you might want to pull KDE into the mix and that would get you the KDE terminal widget. Or you could use KDE Konsole as an alternative to gnome-terminal, which would keep your UI more consistent.
I'm not sure why you wan to launch a terminal to run a command and capture the output. That's what QProcess, or going down a level, popen() is for. QProcess even alows you to capture stderr, which is not as easy with popen(). The only reason you'd want to launch a terminal would be if you needed to get some user input. If you don't need that, then QProcess is probably what you want.
"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown
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When you launch a program via QProcess, it maps the stdin/stdout/stderr to QT stream objects you can read and write to/from. That's fairly straight forward, and I think you understand that.
Now, when you launch a terminal via QProcess, the stdin/stdout/stderr of the terminal get mapped as expected. But what the terminal does is create a pseudo tty (e.g. /dev/pts/n) and uses that for the stdin/stdout/stderr for the process it's running, and displays the results in its window.
visually, something like:
QProcess <=stdin/out=> xterm
+ pty <=stdin/out=> /bin/ls In general, terminal emulators do not forward child program's I/O to its own stdin/out. There might be ways to do that, you'd have to check the manual pages for whatever terminal emulator to see if that's possible.
So this is exactly what happens if you say xterm -e /bin/ps from the command line. In this case, xterm launches, it displays the output of /bin/ps to its screen, and then closes. In the original command line window, nothing gets printed - unless there's output from xterm itself.
Hopefully that explains things a bit for you, and does not add to your confusion.
"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown
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Salvatore Terress wrote: Apparently there are at least two ways to accomplish that.
All languages, C++ or anything else, for an external app has the following communication paths.
- Start Up - Command line parameters.
- Running. Exit code. Which is an int value and nothing else.
- Running. Stdio: stderr, stdin, stdout.
Using the above I have implemented the following in the past
- One computer connecting to multiple hardware devices.
- Error output collected.
- Logging collected.
- Commands controlling each device.
- Binary data sent to and from each device.
An application might provide another API. But that has nothing to do with running it from the first application. And for most standard 'OS Command line' commands it will not apply. As a specific example you can start and stop IIS using command line commands. But you are definitely not going to be accessing web sites from it using exactly the same commands (if at all using a OS command.)
Using a command line app and controlling it requires that one understand exactly what the app does. And that has nothing to do with the controller code from the calling app.
Using a OS shell is going to make the above MUCH harder. That is because the shell must then redirect all output from any commands it runs back along the stdio path (in and out.)
Getting the shell to do that has nothing to do with the calling application. One will need to figure that out by looking for command line parameter to the shell itself. Although I suspect that that it is possible to do this, at the very least I know it is difficult.
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Salvatore Terress wrote: I need to have "sudo" access...
Such access has NOTHING to do with
Linux security.
Yes, it has everything to do with Linux security, as clearly explained in the man page: https://linux.die.net/man/8/sudo[^]. And although I have not tried this myself, I strongly suspect that you cannot use it in the way you are trying to do. If you want elevated/admin permissions then you most likely need to call sudo before you start the original application.
And this question has nothing to do with C/C++; please use the correct forums for your questions.
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