I'd like to use Bash to run a test suite automatically when I save any file in a given directory.
Is there a mechanism for bash to execute a given script on save events?
Thanks.
::EDIT::
I should have mentioned that I'm on using OSX.
Edited: you (the OP) mentioned you use OSX. I'm not aware of any similar tools on OSX. There is a low-level system call (inherited from BSD) called "kqueue", but you'd have to implement your own user-level tool. There is a sample application from Apple, called "Watcher", but it's proof of concept only, and doesn't do what you want.
There is another thread about this on Stack Overflow (also inconclusive).
For lack of an appropriate tool, if you're using a specific programming language, I'd advise you to look for solutions already written for it. Otherwise, I think you're stuck to polling and managing the changes yourself...
Here's my original, Linux-based answer, for archival purposes:
If you're using Linux, you might want to take a look at inotify . More specifically, you can install inotify-tools, which include inotifywait.
With it, you can monitor files and directories for a number of events, such as access, modification, opening, closing and many others. inotifywait can exit once the specified event has been detected, and so a simple loop would get you what you want:
while :; do
inotifywait -e modify /some/directory
run_test_suite
done
By the way, many programming languages and environments already have their own continuous test runners (for instance, with Python you could use tdaemon, among others).
You can use incron to detect when a file has been closed.
Use dnotify only if inotify is not available in Your system (linux kernel < 2.6.13).
dnotify is standard linux method to watch directories:
http://en.wikipedia.org/wiki/Dnotify
Code example. Watch dir for changes:
dnotify WATCH_DIR -M -e SCRIPT_TO_EXECUTE
Please note SCRIPT_TO_EXECUTE will be executed every time, when any file in WATCH_DIR changes.
You can use inotify as explained here Inotify Example: Introduction to Inotify with a C Program Example
Related
I need to run this shell command in a C++ script:
"/usr/local/bin/mjpg_streamer -i "/usr/local/lib/input_uvc.so" -o "/usr/local/lib/output_http.so –w /usr/local/www" -b"
This command launches an application which broadcasts a video feed. When I execute this command via system() in C++ the application doesn't start properly.
I use:
system("/usr/local/bin/mjpg_streamer -i \"/usr/local/lib/input_uvc.so\" -o \"/usr/local/lib/output_http.so –w /usr/local/www\" -b");
When I try to access the video stream after I started it with the C++ application the webpage returns:
501: Not Implemented!
no www-folder configured
I can't expect you guys to give me an application related solution, but I'm wondering if there's a difference in the way commands from a C++ application using system() and commands directly entered in a terminal are executed.
EDIT: The application broadcasts the video stream on IP:8080. I access it by going to that IP in my browser. Usually it opens a webpage with the stream in it but when I execute the command with the C++ application I get that error.
Edit: The old idea of mis-placed quotes was wrong; I realize that -w is actually an option to output_http.so, so the whole shebang must be passed as a single parameter to the -o option, as shown here or here etc.
In that case, check file permissions etc. Does /usr/local/www exist? Is it possible that you are running the shell command from a root shell?
Hey, I have a book recommendation, too, "one of the best tech books ever published": Stevens' Advanced Programming in the Unix Environment. The guy knows -- sorry: knew -- what he was talking about.
I would avoid using the system(3) library function, or at the very least, check its returning error code. I don't understand why you are using " inside your command (I believe that in your particular case, you don't need them; but in general beware of code injection!). Read about globbing
You could use popen(3) to at least get the output of the command.
Even better, code yourself the running of the mjpg_streamer program using the fork(2) & execve(2) & waitpid(2) and other syscalls(2) (perhaps pipe(2), poll(2), dup2(2) etc...). Read Advanced Lnux Programming for more.
It is easier to explain with example.
When 2 text editors edit the same text file in the same time, when one editor saves the file, the other one understands that it was modified and asks to do smth.
How is it possible to get a signal that a file was modified outside the program?
I am working with c++ (though I think it isn't important) and on linux. (solution for windows would be good too)
ISO-C++ does not offer this functionality, so you have to stick with what the operating system provides.
On Linux that would be inotify, on Windows you would use directory change notifications.
① Check the timestamp of the file as close as possible before writing. If it is not what it was when you last opened this file for reading, then beware!
② You can build a checksum of the file and compare this to one you built earlier.
③ Register to a system service which informs you about file activities. This depends on the goodwill of the OS you are using; if this notification service isn't working properly, your stuff will fail. On Linux have a look at Inotify.
I am designing an C++ app that, among other things, executes a few scripts every now and then. The app should be efficient and preferably platform independent.
The issue is, however: is there a reason one shouldn't use system() call for launching scripts and use, for example, POSIX facilities instead? The discussion on the matter that I've seen so far usually boils down to:
system() is less flexible. (Fine with me)
It offers no control of the command being executed. (Fine with me, I just need a return value from the script)
It is not quite platform independent. (Now, this would be a concern. I would really love to see an example where it behaves differently on different platforms)
It is a security concern. (Again, this would be an issue. Can someone provide an example of a potential security problem with system()? )
Any other issues?
3) It is not quite platform independent (Now, this would be a concern. I would really love to see an example where it behaves differently on different platforms)
Well, for instance system("ls") would probably fail in Windows, since there is no ls command.
4) It is a security concern. (Again, this would be an issue. Can someone provide an example of a potential security problem with system() ? )
If the argument passed to system comes from user input, and not properly validated, it can be used to execute unwanted things with the privilege levels of the original executer. If its static content, its quite easy to find that within an executable image and modify it to do nasty things as well.
(3) If you just want a counterexample, for example grep behaves differently on Solaris vs Linux vs whatever.
(4) Your program's privileges are inherited by its spawned programs. If your application ever runs as a privileged user, all someone has to do is put their own program with the name of the thing you shell out too, and then can execute arbitrary code (this implies you should never run a program that uses system as root or setuid root).
(5) It will probably be saner to maintain in the long run to use the posix facilities because you won't have to rely on a specific set of external scripts or binaries already existing wherever your program runs.
I maintain a system that consists of several separate executables. In this case I have control over the permissions, names, calling conventions, security over all supported platforms. In this case, system() works just fine. The applications communicate through a RDBMS.
Again, as others have noted "The Devil's in the details".
Regarding security concerns, a classical example about (4) is the following scenario: imagine the user is prompted to give some directory name to be backed up into a std::string dirname; then you'll compute some backup directory name into a std::string backup and do
system((std::string{"cp -a "} + dirname + " " + backup).c_str())
Now think what happens if a malicious user enter foo bar; rm -rf $HOME; ls as the dirname and backup is /vol/backup_2015_fev/. The system command would execute
cp -a foo bar; rm -rf $HOME; ls /vol/backup_2015_fev/
which is not what you expected (all the user's $HOME would be deleted!). This is an example of code injection, and when using system you should ensure that it never happens (e.g. by sanitizing and/or escaping every user input related string)
Also, the PATH might not be what you believe it is (e.g. starting with /tmp/ and a malicious user having done ln -s /bin/rm /tmp/cp before your system runs).
I used the system() call in my CGI C++ app under windows and Linux too.
One problem I had was when using system() was not having the proper access rights to execute my skript with the web user.
I did not have that problem any more when using the CreateProcess() method.
Whatever command you want to execute just store that in a file c.txt. Pass that file to the execl() like as done below.
fd = open("c.txt", O_CREAT | O_RDWR, 00777);
write(fd,arr,sizeof(arr));
if(fork() == 0)
{
execl("/bin/sh", "sh", "-c","sh c.txt", (char *) 0);
}
I know that in a DOS/Windows application, you can issue system commands from code using lines like:
system("pause");
or
system("myProgram.exe");
...from stdlib.h. Is there a similar Linux command, and if so which header file would I find it in?
Also, is this considered bad programming practice? I am considering trying to get a list of loaded kernal modules using the lsmod command. Is that a good idea or bad idea? I found some websites that seemed to view system calls (at least system("pause");) in a negative light.
system is a bad idea for several reasons:
Your program is suspended until the command finishes.
It runs the command through a shell, which means you have to worry about making sure the string you pass is safe for the shell to evaluate.
If you try to run a backgrounded command with &, it ends up being a grandchild process and gets orphaned and taken in by the init process (pid 1), and you have no way of checking its status after that.
There's no way to read the command's output back into your program.
For the first and final issues, popen is one solution, but it doesn't address the other issues. You should really use fork and exec (or posix_spawn) yourself for running any external command/program.
Not surprisingly, the command is still
system("whatever");
and the header is still stdlib.h. That header file's name means "standard library", which means it's on every standard platform that supports C.
And yes, calling system() is often a bad idea. There are usually more programmatic ways of doing things.
If you want to see how lsmod works, you can always look-up its source code and see what the major system calls are that it makes. Then use those calls yourself.
A quick Google search turns up this link, which indicates that lsmod is reading the contents of /proc/modules.
Well, lsmod does it by parsing the /proc/modules file. That would be my preferred method.
I think what you are looking for are fork and exec.
What Windows API functions are available to execute command prompt's functionality? For example, I like to execute dir command and want to show the output in GUI without using cmd.exe in Windows.
You can start cmd /c dir S:\ome\Path from your process and grab the output. Otherwise it's not possible. But if you're not interested in particular formatting details of dir then you're probably better off just enumerating files/directories and display them.
The dir command is built into the cmd.exe, it's not a separate executable. There's no way of executing it short of running cmd.exe.
EDIT: As for the displaying of results, you need to fill in the STARTUPINFO.hStdXXX members, probably using an anonymous pipe. See this example.
For a console app you can use popen(), but things are by no means so easy from a GUI app. See http://msdn.microsoft.com/en-us/library/ms682499%28VS.85%29.aspx for one approach.
If you want a listing of files in a given folder see this question which describes how to achieve it, using windows api or a more generic boost approach.
Everything the Windows command line does is done through the Win32 APIs.
For example, with regard to "dir", FindFirstFile() and FindNextFile() will give you the contents of a directory.
For any given command, you will need to figure out which APIs/function calls are in use and then learn how to use them yourself in your own code.