Question

I went through the Linux man page for access command, but not sure about the application of the command.

Can someone explain this.

Can it be used like this:

access -f filename;

If i want to check whether the file is existing or not?
But I am getting an error :

The transaction failed: no-cache,

Same thing happens with:

 access -w filename;

if I want to check whether the file is writable by current user.

Also this can also easily be done with test command easily. Then what is the exact difference between these two commands. Please elaborate.
thanks in advance.

Answer 1

That is not a Linux command. It’s C function that can be loaded through the unistd.h library.

You can use it in a C program as follows:

#include <unistd.h>
#include <stdio.h>

int main () {
   int writeable;
   writeable = access("/path/to/file", W_OK);
   if (writeable == -1)
       printf("Not writeable!");
   else
       printf("Writeable!";

   return 0;
}

Note that it returns 0 on success. And 0 is false for C and many other languages, but in this case it means true.

The fact that you can see man access doesn’t mean at all that it’s a Linux command as any standard Linux distribution has man pages for every C library and function. You can also see man malloc. You can determine if it’s a Linux command or a C library man page by viewing the header. For example man access:

ACCESS(2)                  Linux Programmer's Manual                 ACCESS(2)

NAME
       access - check real user's permissions for a file

SYNOPSIS
       #include <unistd.h>

       int access(const char *pathname, int mode);

As you can see, the first line states Linux Programmer's Manual.