1. 관련 코드 분석

1. tlpi-dist/pipes/simple_pipe.c

1. 코드

/* simple_pipe.c

   Simple demonstration of the use of a pipe to communicate
   between a parent and a child process.

   Usage: simple_pipe "string"

   The program creates a pipe, and then calls fork() to create a child process.
   After the fork(), the parent writes the string given on the command line
   to the pipe, and the child uses a loop to read data from the pipe and
   print it on standard output.
*/
#include <sys/wait.h>
#include "tlpi_hdr.h"

#define BUF_SIZE 10

int
main(int argc, char *argv[])
{
    int pfd[2];                             /* Pipe file descriptors */
    char buf[BUF_SIZE];
    ssize_t numRead;

    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s string\n", argv[0]);

    if (pipe(pfd) == -1)                    /* Create the pipe */
        errExit("pipe");

    switch (fork()) {
    case -1:
        errExit("fork");

    case 0:             /* Child  - reads from pipe */
        if (close(pfd[1]) == -1)            /* Write end is unused */
            errExit("close - child");

        for (;;) {              /* Read data from pipe, echo on stdout */
            numRead = read(pfd[0], buf, BUF_SIZE);
            if (numRead == -1)
                errExit("read");
            if (numRead == 0)
                break;                      /* End-of-file */
            if (write(STDOUT_FILENO, buf, numRead) != numRead)
                fatal("child - partial/failed write");
        }

        write(STDOUT_FILENO, "\n", 1);
        if (close(pfd[0]) == -1)
            errExit("close");
        exit(EXIT_SUCCESS);

    default:            /* Parent - writes to pipe */
        if (close(pfd[0]) == -1)            /* Read end is unused */
            errExit("close - parent");

        if (write(pfd[1], argv[1], strlen(argv[1])) != strlen(argv[1]))
            fatal("parent - partial/failed write");

        if (close(pfd[1]) == -1)            /* Child will see EOF */
            errExit("close");
        wait(NULL);                         /* Wait for child to finish */
        exit(EXIT_SUCCESS);
    }
}

2. 동작 모습

3. 디버깅 및 분석

2. tlpi-dist/pipes/popen_glob.c

1. 코드

/* popen_glob.c

   Demonstrate the use of popen() and pclose().

   This program reads filename wildcard patterns from standard input and
   passes each pattern to a popen() call that returns the output from ls(1)
   for the wildcard pattern. The program displays the returned output.
*/
#include <ctype.h>
#include <limits.h>
#include "print_wait_status.h"          /* For printWaitStatus() */
#include "tlpi_hdr.h"

#define POPEN_FMT "/bin/ls -d %s 2> /dev/null"
#define PAT_SIZE 50
#define PCMD_BUF_SIZE (sizeof(POPEN_FMT) + PAT_SIZE)

int
main(int argc, char *argv[])
{
    char pat[PAT_SIZE];                 /* Pattern for globbing */
    char popenCmd[PCMD_BUF_SIZE];
    FILE *fp;                           /* File stream returned by popen() */
    Boolean badPattern;                 /* Invalid characters in 'pat'? */
    int len, status, fileCnt, j;
    char pathname[PATH_MAX];

    for (;;) {                  /* Read pattern, display results of globbing */
        printf("pattern: ");
        fflush(stdout);
        if (fgets(pat, PAT_SIZE, stdin) == NULL)
            break;                      /* EOF */
        len = strlen(pat);
        if (len <= 1)                   /* Empty line */
            continue;

        if (pat[len - 1] == '\n')       /* Strip trailing newline */
            pat[len - 1] = '\0';

        /* Ensure that the pattern contains only valid characters,
           i.e., letters, digits, underscore, dot, and the shell
           globbing characters. (Our definition of valid is more
           restrictive than the shell, which permits other characters
           to be included in a filename if they are quoted.) */

        for (j = 0, badPattern = FALSE; j < len && !badPattern; j++)
            if (!isalnum((unsigned char) pat[j]) &&
                    strchr("_*?[^-].", pat[j]) == NULL)
                badPattern = TRUE;

        if (badPattern) {
            printf("Bad pattern character: %c\n", pat[j - 1]);
            continue;
        }

        /* Build and execute command to glob 'pat' */

        snprintf(popenCmd, PCMD_BUF_SIZE, POPEN_FMT, pat);

        fp = popen(popenCmd, "r");
        if (fp == NULL) {
            printf("popen() failed\n");
            continue;
        }

        /* Read resulting list of pathnames until EOF */

        fileCnt = 0;
        while (fgets(pathname, PATH_MAX, fp) != NULL) {
            printf("%s", pathname);
            fileCnt++;
        }

        /* Close pipe, fetch and display termination status */

        status = pclose(fp);
        printf("    %d matching file%s\n", fileCnt, (fileCnt != 1) ? "s" : "");
        printf("    pclose() status = %#x\n", (unsigned int) status);
        if (status != -1)
            printWaitStatus("\t", status);
    }

    exit(EXIT_SUCCESS);
}

2. 동작 모습