execl/execv/execlp/execle/execvp/execve

函数原型：
       #include
       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[]);
       int execve(const char *path, char *const argv[],
                  char *const envp[]);
一、相同点：
都是exec开头
二、区别：
1. "l"与"v"的区别
    "l"表示参数是列表(list)，形式：const char* argv[0] ,const char* argv[1]......(char*)0
    "v"表示参数是数组(vector)形式：char* const argv[]-----直接用数组名称来作为参数值。
2.”path"与“file”的区别
    path：直接指定可执行文件的路径
    file： 如果里面带有"/"，则表示是文件路径，如果没有，则按照PATH指定的目录路径进行查找可执行文件
3. execle/execve可以传递一个指向环境变量指针数组的指针，而其它函数只能从environ变量中获取

echoall.c

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
    int i;
    char **ptr;
    extern char **environ;

    for(i = 0; i < argc; i++)
        printf("argv[%d]: %s\n",i,argv[i]);

    for(ptr = environ; *ptr != 0; ptr++)
        printf("%s\n",*ptr);

    exit(0);
}

编译:gcc -g echoall.c -o echoall



exec.c

#include <unistd.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

char *env_init[] = { "USER=wgw", "PATH=/tmp",NULL };

int main(void)
{
    pid_t  pid;

    if((pid = fork()) < 0) {
        printf("fork error\n");
    }else if(pid == 0) {
        if(execle("./echoall","echo","myarg1","MY ARG2", (char*)0, env_init) < 0)
            printf("execle error(%d)\n",errno);
    }

    if(waitpid(pid,NULL,0) < 0)
        printf("execle waipid error\n");

    if((pid = fork()) < 0) {
        printf("fork error\n");
    }else if(pid == 0) {
        if(execlp("./echoall","all","only 1 arg", (char*)0) < 0)
            printf("execlp error(%d)\n",errno);
    }
    if(waitpid(pid,NULL,0) < 0)
        printf("execlp waitpid error\n");

    if((pid = fork()) < 0) {
        printf("execl fork error\n");
    }else if(pid == 0) {
        if(execl("./echoall","echoall","MY arg1", "My arg2",(char*)0) < 0)
            printf("execl error(%d)\n",errno);
    }
    exit(0);
}

编译运行：
[e-mail]:~/test/process>./a
argv[0]: echo-------------execle
argv[1]: myarg1
argv[2]: MY ARG2
USER=wgw
PATH=/tmp
argv[0]: all-------------------execlp
argv[1]: only 1 arg
HOSTNAME=hz-dev2.aerohive.com
TERM=linux
SHELL=/bin/bash
HISTSIZE=1000
.............
HOME=/home/gwwu
LOGNAME=gwwu
QTLIB=/usr/lib64/qt-3.3/lib
CVS_RSH=ssh
SSH_CONNECTION=10.155.60.66 55556 10.155.3.246 22
LESSOPEN=|/usr/bin/lesspipe.sh %s
G_BROKEN_FILENAMES=1
_=./a
[e-mail]:~/test/process>argv[0]: echoall--------execl    ////-----父进程未等待子进程，直接退出
argv[1]: MY arg1
argv[2]: My arg2
.................
LOGNAME=gwwu
QTLIB=/usr/lib64/qt-3.3/lib
CVS_RSH=ssh
SSH_CONNECTION=10.155.60.66 55556 10.155.3.246 22
LESSOPEN=|/usr/bin/lesspipe.sh %s
G_BROKEN_FILENAMES=1
_=./a