spawnle()

Spawn a child process, given a list of arguments and an environment

Synopsis:

#include <process.h>

int spawnle( int mode, 
             const char * path, 
             const char * arg0, 
             const char * arg1..., 
             const char * argn, 
             NULL, 
             const char * envp[] );

Arguments:

mode

How you want to load the child process, and how you want the parent program to behave after the child program is initiated:

• P_WAIT — load the child program into available memory, execute it, and make the parent program resume execution after the child process ends.
• P_NOWAIT — execute the parent program concurrently with the new child process.
• P_NOWAITO — execute the parent program concurrently with the new child process. You can't use wait() to obtain the exit code.
• P_OVERLAY — replace the parent program with the child program in memory and execute the child. No return is made to the parent program. This is equivalent to calling the appropriate exec*() function.

path

The full path name of the executable.

arg0, argn, NULL

The arguments that you want to pass to the new process. You must terminate the list with an argument of NULL.

envp

NULL, or a pointer to an array of character pointers, each pointing to a string that defines an environment variable. The array is terminated with a NULL pointer. Each pointer points to a character string of the form:

variable=value
  

that's used to define an environment variable.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The spawnle() function creates and executes a new child process, named in path with NULL-terminated list of arguments in arg0 … argn and with the environment specified in envp. This function calls spawnve().

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If the new child process is a shell script, the first line must start with #!, followed by the path of the program to run to interpret the script, optionally followed by one argument. The script must also be marked as executable. For more information, see “The first line” in the Writing Shell Scripts chapter of the Neutrino User's Guide.

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The spawnle() function isn't a POSIX 1003.1 function, and isn't guaranteed to behave the same on all operating systems. It builds argv[ ] and envp[ ] arrays before calling spawn().

To view the documentation for a function, click its name in this diagram:

Most of the spawn*() functions do a lot of work before a message is sent to procnto.

Arguments are passed to the child process by supplying one or more pointers to character strings as arguments. These character strings are concatenated with spaces inserted to separate the arguments to form one argument string for the child process. At least one argument, arg0, must be passed to the child process. By convention, this first argument is a pointer to the name of the new child process.

If envp is NULL, the child process inherits the environment of the parent process. The new process can access its environment by using the environ global variable (found in <unistd.h>).

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A parent/child relationship doesn't imply that the child process dies when the parent process dies.

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Returns:

The spawnle() function's return value depends on the mode argument:

If an error occurs, -1 is returned (errno is set).

Errors:

E2BIG

The number of bytes used by the argument list or environment list of the new child process is greater than ARG_MAX bytes.

EACCESS

Search permission is denied for a directory listed in the path prefix of the new child process or the new child process's file doesn't have the execute bit set.

EAGAIN

Insufficient resources available to create the child process.

EBADF

An error occurred duplicating open file descriptors to the new process.

EFAULT

One of the buffers specified in the function call is invalid.

ELOOP

Too many levels of symbolic links or prefixes.

EMFILE

Insufficient resources available to load the new executable image or to remap file descriptors in the child process.

ENAMETOOLONG

The length of path exceeds PATH_MAX or a pathname component is longer than NAME_MAX.

ENOENT

The file identified by the path argument is empty, or one or more components of the pathname of the child process don't exist.

ENOEXEC

The child process's file has the correct permissions, but isn't in the correct format for an executable.

ENOMEM

Insufficient memory available to create the child process.

ENOSYS

The spawnle() function isn't implemented for the filesystem specified in path.

ENOTDIR

A component of the path prefix of the child process isn't a directory.

Examples:

Run myprog as if the user had typed:

myprog ARG1 ARG2

at the command-line:

#include <stddef.h>
#include <process.h>

char *env_list[] = { "SOURCE=MYDATA",
             "TARGET=OUTPUT",
             "lines=65",
             NULL
            };

spawnle( P_WAIT, "myprog",
    "myprog", "ARG1", "ARG2", NULL,
     env_list );

The program is found if myprog is in the current working directory. The environment for the child program consists of the three environment variables SOURCE, TARGET and lines.

Classification:

QNX 4

Caveats:

If mode is P_WAIT, this function is a cancellation point.

See also:

execl(), execle(), execlp(), execlpe(), execv(), execve(), execvp(), execvpe(), getenv(), putenv(), setenv(), spawn(), spawnl(), spawnlp(), spawnlpe(), spawnp(), spawnv(), spawnve(), spawnvp(), spawnvpe(), wait(), waitpid()

Processes and Threads chapter of Getting Started with QNX Neutrino