How to Check Directory Existence in Unix Using System Calls?

Checking Directory Existence in Unix: A Comprehensive Guide Using System Calls

Problem:

In Unix, how can one determine the existence of a directory using a system call without opening it or handling related errors?

Answer:

POSIX systems provide two essential functions for this purpose: stat() and lstat(). These functions allow you to ascertain whether a pathname reflects a valid accessible object and retrieve information about its type.

Key Differences Between stat() and lstat():

• stat(): Follows symbolic links and provides information about the final destination.
• lstat(): Provides information about the symbolic link itself, regardless of any targets it may point to.

Implementation Using stat():

#include <sys/stat.h>

struct stat sb;

if (stat(pathname, &sb) == 0 && S_ISDIR(sb.st_mode)) {
    // True if pathname is a directory
}

Additional File Type Verification:

Using the S_IS* macros from , you can verify other file types beyond directories:

• S_ISREG: Regular file
• S_ISCHR: Character device
• S_ISBLK: Block device
• S_ISFIFO: FIFO
• S_ISLNK: Symbolic link
• S_ISSOCK: Socket

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