dirs_links/view_symlink.c

This is dirs_links/view_symlink.c (Listing 18-4, page 369), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, 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
+/* view_symlink.c
+
+   Demonstrate the use of readlink() and realpath() to read and display
+   the contents of a symbolic link.
+*/
 #include <sys/stat.h>
 #include <limits.h>             /* For definition of PATH_MAX */
 #include "tlpi_hdr.h"
 
 #define BUF_SIZE PATH_MAX
 
 int
 main(int argc, char *argv[])
 {
     struct stat statbuf;
     char buf[BUF_SIZE];
     ssize_t numBytes;
 
     if (argc != 2 || strcmp(argv[1], "--help") == 0)
         usageErr("%s pathname\n", argv[0]);
 
+    /* User lstat() to check whether the supplied pathname is
+       a symbolic link. Alternatively, we could have checked to
+       whether readlink() failed with EINVAL. */
+
     if (lstat(argv[1], &statbuf) == -1)
         errExit("lstat");
 
     if (!S_ISLNK(statbuf.st_mode))
         fatal("%s is not a symbolic link", argv[1]);
 
     numBytes = readlink(argv[1], buf, BUF_SIZE - 1);
     if (numBytes == -1)
         errExit("readlink");
     buf[numBytes] = '\0';                       /* Add terminating null byte */
     printf("readlink: %s --> %s\n", argv[1], buf);
 
     if (realpath(argv[1], buf) == NULL)
         errExit("realpath");
     printf("realpath: %s --> %s\n", argv[1], buf);
 
     exit(EXIT_SUCCESS);
 }

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