Inter-process communication between embedded Linux (II.)--exec family functions

Inter-process communication between embedded Linux (II.)--exec family function

exec The function family does this by locating the executable file according to the specified file name and substituting it for the contents of the calling process, in other words, executing an executable file inside the calling process. The executable file here can be either a binary file or a script file that can be executed under any Linux .

The exec family functions include the following functions:

#include <unistd.h>

extern char **environ;

int execl (const char *path, const char *arg, ...);

int EXECLP (const char *file, const char *arg, ...);

int execle (const char *path, const char *arg,

..., char * const envp[]);

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

int EXECVP (const char *file, char *const argv[]);

The difference between execl and execv is that the parameters are passed differently,execl The parameters in a list,execv The parameters are stored in a string array. EXECLP and execvp Add the path to the file lookup, first find the path parameter of the file, the environment variable is not found PATH to find. execle adds an array of strings to the executable program passing environment variables.

Examples of function use:

Execl ("/bin/ls", "ls", "-a", "-l", NULL);

Char *const arg[] = {"ls", "-L", "-a", NULL};

EXECV ("/bin/ls", Arg);

EXECVP ("LS", ARG);

Execle usage Examples:

EXEC.C: Compile build exec

#include <stdio.h>

#include <unistd.h>

int main (int argc, char **argv)

{

Char *const envp[] = {"Name=scorpio", "host=192.168.6.200", NULL};

Execle ("./hello", "Hello", NULL, ENVP);

return 0;

}

HELLO.C: Compile build Hello

#include <stdio.h>

#include <unistd.h>

extern char **environ;

int main (int argc, char **argv)

{

printf ("hello\n");

int i = 0;

for (i = 0; Environ[i]! = NULL; i++)

{

printf ("%s\n", Environ[i]);

}

return 0;

}

Run ./exec:

Hello

Name=scorpio

host=192.168.6.200

The environment variables defined in the EXEC program are passed to the calling Hello program.

Common errors:

A, The file or path cannot be found, at which point errno is set to Enoent

b, array and ENVP forget to use null errno is set to efault

C, there is no permission to run the file to execute , at which point errno is set to eacces

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Inter-process communication between embedded Linux (II.)--exec family functions