Execute a system command
#include <stdlib.h> int system( const char *command );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The behavior of the system() function depends on the value of its command argument:
This means that any command that can be entered to the OS can be executed, including programs, QNX Neutrino commands, and shell scripts. The exec*() and spawn*() functions can only cause programs to be executed.
For example, assume that status is the value returned by system(). If WEXITSTATUS( status ) returns 255, either the specified command returned a termination status of 255, or the shell didn't exit (i.e., it died from a signal or couldn't be started at all) and the return value was 255 due to implementation details. For example, under QNX Neutrino and most Unix systems, the value is 255 if status is -1, which indicates that the shell couldn't be executed. WEXITSTATUS() is defined in <sys/wait.h>.
For information about macros that extract information from the value returned by system(), see “Status macros” in the description of wait().
When an error has occurred, errno contains a value that indicates the type of error that has been detected. In particular, see the error codes for spawn().
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>
int main( void )
{
int rc;
rc = system( "ls" );
if( rc == -1 ) {
printf( "shell could not be run\n" );
} else {
printf( "result of running command is %d\n",
WEXITSTATUS( rc ) );
}
return EXIT_SUCCESS;
}
| Safety: | |
|---|---|
| Cancellation point | Yes |
| Interrupt handler | No |
| Signal handler | No |
| Thread | Yes |