pipes/popen_glob.c

This is pipes/popen_glob.c (Listing 44-5, page 904), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* 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);
}

 

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