Questions tagged [execvp]

execvp is a POSIX function, from the exec* family, which replaces the current process with one specified.

It is available on most every UNIX-like platform, including Linux and Mac OS X, where a unistd.h file exists, and many languates, such as Python, emulate this function on platforms, such as Windows, where this function does not normally exist. Many languages, including C, C++, and Python, have interfaces to this function.

If it succeeds, it will not return and the current process will be replaced. If it does not succeed, then it will return a -1.

POSIX specifies that this function has the signature:

int execvp(const char *path, char *const argv[]);.

Its arguments are interpreted as follows.:

• path: This is a NULL terminated string which holds the name of an executable. It is specified that execvp will search the PATH environment variable for this name if it is not a path.

  If it is a path, then execvp will look for the executable where specified, using an absolute path if this argument begins with a /, or a relative one if this argument doesn't.

Example: ping will resolve to /bin/ping.

• argv: This is an array of NULL terminated strings, which make up the argv of the process in the path argument.

  This array should end with a NULL, and should start with the name of the executable passed in the path argument.

Example: {"ping", "-c", "5", "www.google.com", NULL}

POSIX includes the following complete example for reference:

The following example illustrates the use of execvp to execute the ls shell command:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

main()
{    
     pid_t pid;
     char *const parmList[] = {"/bin/ls", "-l", "/u/userid/dirname", NULL};

     if ((pid = fork()) == -1)
          perror("fork() error");    
     else if (pid == 0) {
          execvp("ls", parmList);
          printf("Return not expected. Must be an execvp() error.\n");    
     }
}