进程和程序

execvp(const char *file,const char *argv);

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

 #define MAXARGS     20
 #define ARGLEN         100

int main(void)
{
    char *arglist[MAXARGS+1];
    int numargs;
    char argbuf[ARGLEN];
    char *makestring();

    numargs=0;

    while(numargs < MAXARGS)
    {
        printf("Arg[%d]:",numargs);
        if(fgets(argbuf,ARGLEN,stdin) && *argbuf != '\n')
            arglist[numargs++]=makestring(argbuf);
        else
        {
            if(numargs>0)
            {
                arglist[numargs]=NULL;
                execute(arglist);
                numargs=0;
            }
        }
    }
    return 0;
}

int execute(char *arglist[])
{
    execvp(arglist[0],arglist);
    perror("execvp failed");
    exit(1);
}

char *makestring(char *buf)
{
    char *cp;
    buf[strlen(buf)-1]='\0';
    cp=(char *)malloc(strlen(buf)+1);
    if(cp==NULL)
    {
        fprintf(stderr,"no memory\n");
        exit(1);
    }
    strcpy(cp,buf);
    return cp;
}

 pid_t result=fork(void);

#include <unistd.h>
#include <stdio.h>

int main(void)
{
    int ret_from_fork,mypid;

    mypid=getpid();
    printf("Before:my pid is %d\n",mypid);

    ret_from_fork=fork();

    sleep(1);

    printf("After my pid id %d,fork() said %d\n",getpid(),ret_from_fork);
}

#include <unistd.h>
#include <stdio.h>

int main(void)
{
    printf("my pid is %d\n",getpid());
    fork();
    fork();
    fork();
    printf("my pid is %d\n",getpid());
}

#include <unistd.h>
#include <stdio.h>

int main(void)
{
    int fork_rv;
    printf("before %d\n",getpid());
    fork_rv=fork();

    if(fork_rv==-1)
        perror("fork");
    else if(fork_rv==0)
        printf("child:%d\n",getpid());
    else
        printf("parent:%d,my child is %d\n",getpid(),fork_rv);
}

#include <sys/types.h>

#include <sys/wait.h>

pid_t result=wait(int *status);

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

#define DELAY 2

int main(void)
{
    int newpid;
    void child_code(),parent_code();

    printf("before:my pid is %d\n",getpid());
    if((newpid=fork())==-1)
        perror("fork");
    else if(newpid==0)
        child_code(DELAY);
    else 
        parent_code(newpid);
}

void child_code(int delay)
{
    printf("child %d here,will sleep for %d seconds\n",getpid(),delay);
    sleep(delay);
    printf("child done about to exit\n");
    exit(17);
}

void parent_code(int childpid)
{
    int wait_rv;
    wait_rv=wait(NULL);
    printf("done waiting for %d,wait returned %d\n",childpid,wait_rv);
}

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

#define DELAY 5

void child_code();
void parent_code();
int main(void)
{
    pid_t newpid;
    printf("before:my pid is %d\n",getpid());

    if((newpid=fork())==-1)
        perror("fork");
    else if(newpid==0)
        child_code(DELAY);
    else
        parent_code();
}

void child_code(int delay)
{
    printf("child %d here will sleep for %d seconds\n",getpid(),delay);
    sleep(delay);
    printf("child done\n");
    exit(17);
}

void parent_code(int childpid)
{
    int wait_rv;
    int child_status;
    int high_8,low_7,bit_7;

    wait_rv=wait(&child_status);
    printf("done waiting for %d,wait return %d\n",childpid,wait_rv);

    high_8=child_status>>8;
    low_7=child_status & 0x7F;
    bit_7=child_status & 0x80;
    printf("status:exit=%d,sig=%d,core=%d\n",high_8,low_7,bit_7);
}

shell:

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

#define MAXARGS     20
#define ARGLEN         100

char *makestring(char *argbuf);
void execute(char *arglist[]);

int main(void)
{
    char *arglist[MAXARGS+1];
    int numargs=0;
    char argbuf[ARGLEN];
    while(numargs < MAXARGS)
    {
        printf("Arg[%d]:",numargs);
        if(fgets(argbuf,ARGLEN,stdin) && *argbuf != '\n')
            arglist[numargs++]=makestring(argbuf);
        else
        {
            if(numargs > 0)
            {
                arglist[numargs]=NULL;
                execute(arglist);
                numargs=0;
            }
        }
    }
    return 0;
}


char *makestring(char *argbuf)
{
    char *cp;
    argbuf[strlen(argbuf)-1]='\0';
    cp=(char *)malloc(strlen(argbuf)+1);
    if(cp==NULL)
    {
        fprintf(stderr,"no memory\n");
        exit(1);
    }
    strcpy(cp,argbuf);
    return cp;
}

void execute(char *arglist[])
{
    int pid,exitstatus;
    pid=fork();

    switch(pid)
    {
        case -1:
            perror("fork error");
            exit(1);
        case 0:
            execvp(arglist[0],arglist);
            perror("execvp failed");
            exit(1);
        default:
            while(wait(&exitstatus) != pid)
                ;
        printf("child exited with status %d,%d\n",exitstatus>>8,exitstatus &0377);
    }
}