如何从存储 C 中 shell 脚本的 output 的指针获取多个字符串？

Question

I am trying to write a code in C with named pipes (fifo), where the client is asking for information about a directory.

The server checks for the existence of the directory, and sends back the size of the directory, and the number of files and subdirectories. The request can also specify to get the name of the files and subdirectories.

The client gets the name of the directory as an argument, also the specification by -d option. The server executes a shell script in order to solve the problem.

I already asked a question about this topic and got some improvements in the code, but still can't get it running correctly.

Here is the link to the question: How to pass multiple arguments to client (fifo)?

My problem is now that the server prints out only one file name instead of all filenames and subdirectories inside the directory that was given as an argument to the client.

Here is the modified server code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include "header.h"

int f;
Message msg;

int main() {
    if (mkfifo(FIFONAME, S_IFIFO | 0666) < 0) { /*Creating server fifo*/
        perror("Failed creating own fifo");
        printf("Server: Failed creating fifo_%d file\n", getpid());
        unlink(FIFONAME);
        exit(1);
    }

    if ((f = open(FIFONAME, O_RDONLY)) < 0) {
        perror("Failed opening fifo");
        unlink(FIFONAME);
        exit(1);
    }       

    printf("Server is working\n");
    while (1) { /*Infinite loop, waiting for client requests*/
        if ((read(f, &msg, sizeof(msg)))) {
            if (strcmp(msg.dir, "exit") == 0) {
                close(f);
                unlink(FIFONAME);
                exit(1);
            }

            switch (fork()) {
              case -1: {
                perror("Fork error\n");
                exit(1);
              }

              case 0: {
                char command[MAXLEN];
                sprintf(command,"./shell.sh %s %s", msg.dir, msg.spec);
                FILE *g;
                if ((g = popen(command, "r")) == NULL) {
                    perror("Popen error");
                    exit(1);
                }

                fgets(msg.dir, MAXLEN, g);
                fgets(msg.spec, MAXLEN, g);
                char result[MAXLEN];
                sprintf(result, "fifo_%d", msg.pid);
                msg.pid = getpid();
                int op;
                op = open(result, O_WRONLY);
                write(op, &msg, sizeof(msg));
                close(op);
                exit(0);
              }
            }
        }
    }
    return 0;
}

And the client code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include "header.h"

int f, fc;
Message msg;
char fifoname[MAXLEN];

int main(int argc, char *argv[]) {
    if (argc == 1) {
        printf("Usage: %s directory name\n",argv[0]);
        exit(1);
    }
    sprintf(fifoname, "fifo_%d", getpid());
    if (strcmp(argv[1], "0"))
        if (mkfifo(fifoname, S_IFIFO | 0666) < 0) { /*Creating own FIFO file for result*/
            perror("Failed creating own clientfifo");
            printf("Client error: Failed creating fifo_%d file\n", getpid());
            exit(2);
        }

    if ((f = open(FIFONAME, O_WRONLY)) < 0) { /*Opening serverfifo for writing*/
        perror("Failed connecting to server");
        exit(3);
    }

    strcpy(msg.dir, argv[1]);
    strcpy(msg.spec, argv[2]); 
    msg.pid = getpid();
    write(f, &msg, sizeof(msg));

    if (strcmp(argv[1], "exit")) { /* The client is not expecting any result 
                                      because the server stopped*/
        if ((fc = open(fifoname, O_RDONLY)) < 0) { /*Opening own fifo for reading*/
            perror("Failed opening own fifo");
            printf("Client error: Failed opening own %s file\n", fifoname);
            exit(4);        
        }
        read(fc, &msg, sizeof(msg));
        printf("Client %d, received: %s%s\n", getpid(), msg.dir, msg.spec);
        close(fc);
    }

    unlink(fifoname);
    close(f);
    exit(0);
}

The common header file:

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

#define FIFONAME "server_fifo"
#define MAXLEN 1000

typedef struct {
    int pid; /*folyamat azonositoja*/
    char dir[MAXLEN];
    char spec[MAXLEN];
} Message;

And the output I get is:

-bash-4.1$ ./client dir -d
Client 42723, received: 16K,2 directories, 2 files
a

While it should look like this:

-bash-4.1$ ./client dir -d
Client 42723, received: 16K,2 directories, 2 files
a
b
dir1
dir2

What needs to be modified in order to get the full output?

Answer 1

The problem is at line 52 inside server.c.
You are using fgets() to copy the output to msg.spec . But fgets() stops taking input at newline charater ('\n').
Hence you only see one result.

To overcome this, you can do something like:

char str[100]; // arbitrary length
while(fgets(str, MAXLEN, g))
{
     strcat(msg.spec, str);
}

This keeps taking input every iteration and concatenates each line to previous output.