access()

Check to see if a file or directory can be accessed

Synopsis:

#include <unistd.h>

int access( const char * path,
            int amode );

Library:

libc

Description:

The access() function checks if the file or directory specified by path exists and if it can be accessed with the file access permissions given by amode. However, unlike other functions (open() for example), it uses the real user ID and real group ID in place of the effective user and group IDs.

The value of amode is either:

F_OK

Test for file existence.

or a bitwise ORing of the following access permissions to be checked, as defined in the header <unistd.h>:

R_OK

Test for read permission.

W_OK

Test for write permission.

X_OK

For a directory, test for search permission. Otherwise, test for execute permission.

Returns:

0

The file or directory exists and can be accessed with the specified mode.

-1

An error occurred (errno is set).

Errors:

EACCES

The permissions specified by amode are denied, or search permission is denied on a component of the path prefix.

EINVAL

An invalid value was specified for amode.

ELOOP

Too many levels of symbolic links or prefixes.

ENAMETOOLONG

The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.

ENOENT

A component of the path isn't valid.

ENOSYS

The access() function isn't implemented for the filesystem specified in path.

ENOTDIR

A component of the path prefix isn't a directory.

EROFS

Write access was requested for a file residing on a read-only file system.

Examples:

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

int main( int argc, char **argv )
  {
    if( argc!= 2 ) {
      fprintf( stderr, 
        "use: readable <filename>\n" );
      return EXIT_FAILURE;
    }

    if( !access( argv[1], R_OK ) ) {
      printf( "ok to read %s\n", argv[1] );
      return EXIT_SUCCESS;
    } else {
      perror( argv[1] );
      return EXIT_FAILURE;
    }
  }

Classification:

POSIX 1003.1

See also:

chmod(), eaccess, errno, fstat(), open(), stat()