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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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

  Cover of The Linux Programming Interface
+/* 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)
 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: ");
         if (fgets(pat, PAT_SIZE, stdin) == NULL)
             break;                      /* EOF */
         len = strlen(pat);
         if (len <= 1)                   /* Empty line */
         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]);
         /* 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");
         /* Read resulting list of pathnames until EOF */
         fileCnt = 0;
         while (fgets(pathname, PATH_MAX, fp) != NULL) {
             printf("%s", pathname);
         /* 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);

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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