Execute a file
#include <unistd.h> int execl( const char * path, const char * arg0, const char * arg1, … const char * argn, NULL );
This function is declared in <process.h>, which <unistd.h> includes.
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The execl() function replaces the current process image with a new process image specified by path. The new image is constructed from a regular, executable file called the new process image file. No return is made because the calling process image is replaced by the new process image.
When a C-language program is executed as a result of this call, it's entered as a C-language function call as follows:
int main (int argc, char *argv);
where argc is the argument count and argv is an array of character pointers to the arguments themselves. In addition, the following variable:
extern char **environ;
is initialized as a pointer to an array of character pointers to the environment strings. The argv and environ arrays are each terminated by a null pointer. The null pointer terminating the argv array isn't counted in argc.
Multithreaded applications shouldn't use the environ variable to access or modify any environment variable while any other thread is concurrently modifying any environment variable. A call to any function dependent on any environment variable is considered a use of the environ variable to access that environment variable.
The arguments specified by a program with one of the exec* functions are passed on to the new process image in the corresponding main() arguments.
The number of bytes available for the new process's combined argument and environment lists is ARG_MAX.
File descriptors open in the calling process image remain open in the new process image, except for when fcntl()'s FD_CLOEXEC flag is set. For those file descriptors that remain open, all attributes of the open file description, including file locks remain unchanged. If a file descriptor is closed for this reason, file locks are removed as described by close() while locks not affected by close() aren't changed.
Directory streams open in the calling process image are closed in the new process image.
Signals set to SIG_DFL in the calling process are set to the default action in the new process image. Signals set to SIG_IGN by the calling process images are ignored by the new process image. Signals set to be caught by the calling process image are set to the default action in the new process image.
After a successful call, any functions previously registered by atexit() are no longer registered.
If the path is on a filesystem mounted with the ST_NOSUID flag set, the effective user ID, effective group ID, saved set-user ID and saved set-group ID are unchanged for the new process. Otherwise, if the set-user ID mode bit is set, the effective user ID of the new process image is set to the user ID of path. Similarly, if the set-group ID mode bit is set, the effective group ID of the new process is set to the group ID of path. The real user ID, real group ID, and supplementary group IDs of the new process remain the same as those of the calling process. The effective user ID and effective group ID of the new process image are saved (as the saved set-user ID and the saved set-group ID used by setuid()).
Any shared memory segments attached to the calling process image aren't attached to the new process image. If the calling process had locked any memory, the locks are released.
The new process also inherits at least the following attributes from the calling process image:
If you call this function from a process with more than one thread, all of the threads are terminated and the new executable image is loaded and executed. No destructor functions are called.
Upon successful completion, the st_atime field of the file is marked for update. If the exec* function failed but was able to locate the process image file, whether the st_atime field is marked for update is undefined. On success, the process image file is considered to be opened with open(). The corresponding close() is considered to occur at a time after this open, but before process termination or successful completion of a subsequent call to one of the exec* functions.
|execl()||NULL-terminated argument list||Yes|
|execle()||NULL-terminated argument list, specify the new process environment||Yes|
|execlp()||NULL-terminated argument list, search for the new process in PATH||Yes|
|execlpe()||NULL-terminated argument list, search for the new process in PATH, specify the new process environment||No|
|execv()||NULL-terminated array of arguments||Yes|
|execve()||NULL-terminated array of arguments, specify the new process environment||Yes|
|execvp()||NULL-terminated array of arguments, search for the new process in PATH||Yes|
|execvpe()||NULL-terminated array of arguments, search for the new process in PATH, specify the new process environment||No|
When execl() is successful, it doesn't return; otherwise, it returns -1 (errno is set).
Replace the current process with myprog as if a user had typed:
myprog ARG1 ARG2
at the shell:
#include <stddef.h> #include <unistd.h> execl( "myprog", "myprog", "ARG1", "ARG2", NULL );
In this example, myprog will be found if it exists in the current working directory.
abort(), atexit(), errno, execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), _exit(), exit(), getenv(), main(), putenv(), spawn(), spawnl(), spawnle(), spawnlp(), spawnlpe(), spawnp(), spawnv(), spawnve(), spawnvp(), spawnvpe(), system()
Processes and Threads chapter of Getting Started with QNX Neutrino