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Search found 7 results on 1 pages for 'execv'.

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• Writing own Unix shell in C - Problems with PATH and execv

  - by user1287523

  I'm writing my own shell in C. It needs to be able to display the users current directory, execute commands based on the full path (must use execv), and allow the user to change the directory with cd. This IS homework. The teacher only gave us a basic primer on C and a very brief skeleton on how the program should work. Since I'm not one to give up easily I've been researching how to do this for three days, but now I'm stumped. This is what I have so far: Displays the user's username, computername, and current directory (defaults to home directory). Prompts the user for input, and gets the input Splits the user's input by " " into an array of arguments Splits the environment variable PATH by ":" into an array of tokens I'm not sure how to proceed from here. I know I've got to use the execv command but in my research on google I haven't really found an example I understand. For instance, if the command is bin/ls, how does execv know the display all files/folders from the home directory? How do I tell the system I changed the directory? I've been using this site a lot which has been helpful: http://linuxgazette.net/111/ramankutty.html but again, I'm stumped. Thanks for your help. Let me know if I should post some of my existing code, I'm wasn't sure if it was necessary though.

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• convert string to argv in c++

  - by aaronstacy

  I have an std::string containing a command to be executed with execv, what is the best "C++" way to convert it to the "char *argv[]" that is required by the second parameter of execv()? To clarify: std::string cmd = "mycommand arg1 arg2"; char *cmd_argv[]; StrToArgv(cmd, cmd_argv); // how do I write this function? execv(cmd_argv[0], cmd_argv);

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• What to do if exec() fails?

  - by Grigory

  Let's suppose we have a code doing something like this: int pipes[2]; pipe(pipes); pid_t p = fork(); if(0 == p) { dup2(pipes[1], STDOUT_FILENO); execv("/path/to/my/program", NULL); ... } else { //... parent process stuff } As you can see, it's creating a pipe, forking and using the pipe to read the child's output (I can't use popen here, because I also need the PID of the child process for other purposes). Question is, what should happen if in the above code, execv fails? Should I call exit() or abort()? As far as I know, those functions close the open file descriptors. Since fork-ed process inherits the parent's file descriptors, does it mean that the file descriptors used by the parent process will become unusable?

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• Running "source" from python

  - by R S

  Hello, I have a file a.txt with lines of commands I want to run, say: echo 1 echo 2 echo 3 If I was on csh (unix), I would have done source a.txt and it would run. From python I want to run os.execl with it, however I get: >>> os.execl("source", "a.txt") Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/lib/python2.5/os.py", line 322, in execl execv(file, args) OSError: [Errno 2] No such file or directory How to do it?

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• how can exec change the behavior of exec'ed program

  - by R Samuel Klatchko

  I am trying to track down a very odd crash. What is so odd about it is a workaround that someone discovered and which I cannot explain. The workaround is this small program which I'll refer to as 'runner': #include <stdio.h> #include <unistd.h> #include <string.h> #include <errno.h> int main(int argc, char *argv[]) { if (argc == 1) { fprintf(stderr, "Usage: %s prog [args ...]\n", argv[0]); return 1; } execvp(argv[1], argv + 1); fprintf(stderr, "execv failed: %s\n", strerror(errno)); // If exec returns because the program is not found or we // don't have the appropriate permission return 255; } As you can see, all this program does is use execvp to replace itself with a different program. The program crashes when it is directly invoked from the command line: /path/to/prog args # this crashes but works fine when it is indirectly invoked via my runner shim: /path/to/runner /path/to/prog args # works successfully For the life of me, I can figure out how having an extra exec can change the behavior of the program being run (as you can see the program does not change the environment). Some background on the crash. The crash itself is happening in the C++ runtime. Specifically, when the program does a throw, the crashing version incorrectly thinks there is no matching catch (although there is) and calls terminate. When I invoke the program via runner, the exception is properly caught. My question is any idea why the extra exec changes the behavior of the exec'ed program?

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• what is the relation between SIGTSTP and SIGCHLD

  - by Rawhi

  I have tow handlers for each one of them (SIGTSTP, SIGCHLD), the thing is that when I pause a process using SIGTSTP the handler function of SIGCHLD run too. what should I do to prevent this . void ExeExternal(char *args[MAX_ARG], char* cmdString, LIST_ELEMENT** pList, int *Susp_Bg_Pid, int *susp) { int pID, status, w; switch (pID = fork()) { case -1: perror("smash error: >"); break; case 0: // Child Process setpgrp(); execv(args[0], args); execvp(args[0], args); perror("error"); exit(EXIT_FAILURE); break; default: if (cmdString[strlen(cmdString) - 1] != '&') { *Susp_Bg_Pid = pID; *susp = 1; while(*susp); } else { InsertElem(pList, args[0], getpid(), pID, 0); } break; } } signal handlers : void signalHandler(int signal) { int pid, cstatus; if (signal == SIGCHLD) { susp = 0; pid = waitpid(-1, &cstatus, WNOHANG); printf("[[child %d terminated]]\n", pid); DelPID(&JobsList, pid); } } void ctrlZsignal(int signal){ kill(Susp_Bg_Pid, SIGTSTP); susp = 0; printf("\nchild %d suspended\n", Susp_Bg_Pid); } Susp_Bg_Pid used to save the paused process id. susp indicates the state of the "smash" the parent process if it is suspended or not .

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• How to get an X11 Window from a Process ID ?

  - by Adam Pierce

  Under Linux, my C++ application is using fork() and execv() to launch multiple instances of OpenOffice so as to view some powerpoint slide shows. This part works. Next I want to be able to move the OpenOffice windows to specific locations on the display. I can do that with the XMoveResizeWindow() function but I need to find the Window for each instance. I have the process ID of each instance, how can I find the X11 Window from that ? UPDATE - Thanks to Andy's suggestion, I have pulled this off. I'm posting the code here to share it with the Stack Overflow community. Unfortunately Open Office does not seem to set the _NET_WM_PID property so this doesn't ultimately solve my problem but it does answer the question. // Attempt to identify a window by name or attribute. // by Adam Pierce <[email protected]> #include <X11/Xlib.h> #include <X11/Xatom.h> #include <iostream> #include <list> using namespace std; class WindowsMatchingPid { public: WindowsMatchingPid(Display *display, Window wRoot, unsigned long pid) : _display(display) , _pid(pid) { // Get the PID property atom. _atomPID = XInternAtom(display, "_NET_WM_PID", True); if(_atomPID == None) { cout << "No such atom" << endl; return; } search(wRoot); } const list<Window> &result() const { return _result; } private: unsigned long _pid; Atom _atomPID; Display *_display; list<Window> _result; void search(Window w) { // Get the PID for the current Window. Atom type; int format; unsigned long nItems; unsigned long bytesAfter; unsigned char *propPID = 0; if(Success == XGetWindowProperty(_display, w, _atomPID, 0, 1, False, XA_CARDINAL, &type, &format, &nItems, &bytesAfter, &propPID)) { if(propPID != 0) { // If the PID matches, add this window to the result set. if(_pid == *((unsigned long *)propPID)) _result.push_back(w); XFree(propPID); } } // Recurse into child windows. Window wRoot; Window wParent; Window *wChild; unsigned nChildren; if(0 != XQueryTree(_display, w, &wRoot, &wParent, &wChild, &nChildren)) { for(unsigned i = 0; i < nChildren; i++) search(wChild[i]); } } }; int main(int argc, char **argv) { if(argc < 2) return 1; int pid = atoi(argv[1]); cout << "Searching for windows associated with PID " << pid << endl; // Start with the root window. Display *display = XOpenDisplay(0); WindowsMatchingPid match(display, XDefaultRootWindow(display), pid); // Print the result. const list<Window> &result = match.result(); for(list<Window>::const_iterator it = result.begin(); it != result.end(); it++) cout << "Window #" << (unsigned long)(*it) << endl; return 0; }

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