25.6.4 File Attributes

This section describes the functions for getting detailed information about a file, including the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.

Function: file-newer-than-file-p filename1 filename2

This function returns t if the file filename1 is newer than file filename2. If filename1 does not exist, it returns nil. If filename1 does exist, but filename2 does not, it returns t.

In the following example, assume that the file aug-19 was written on the 19th, aug-20 was written on the 20th, and the file no-file doesn’t exist at all.

(file-newer-than-file-p "aug-19" "aug-20")
     ⇒ nil

(file-newer-than-file-p "aug-20" "aug-19")
     ⇒ t

(file-newer-than-file-p "aug-19" "no-file")
     ⇒ t

(file-newer-than-file-p "no-file" "aug-19")
     ⇒ nil

Function: file-attributes filename &optional id-format

This function returns a list of attributes of file filename. If the specified file’s attributes cannot be accessed, it returns nil. This function does not follow symbolic links. The optional parameter id-format specifies the preferred format of attributes UID and GID (see below)—the valid values are 'string and 'integer. The latter is the default, but we plan to change that, so you should specify a non-nil value for id-format if you use the returned UID or GID.

On GNU platforms when operating on a local file, this function is atomic: if the filesystem is simultaneously being changed by some other process, this function returns the file’s attributes either before or after the change. Otherwise this function is not atomic, and might return nil if it detects the race condition, or might return a hodgepodge of the previous and current file attributes.

Accessor functions are provided to access the elements in this list. The accessors are mentioned along with the descriptions of the elements below.

The elements of the list, in order, are:

0. t for a directory, a string for a symbolic link (the name linked to), or nil for a text file (file-attribute-type).
1. The number of names the file has (file-attribute-link-number). Alternate names, also known as hard links, can be created by using the add-name-to-file function (see Changing Files).
2. The file’s UID, normally as a string (file-attribute-user-id). However, if it does not correspond to a named user, the value is a number.
3. The file’s GID, likewise (file-attribute-group-id).
4. The time of last access, as a list of four integers (sec-high sec-low microsec picosec) (file-attribute-access-time). (This is similar to the value of current-time; see Time of Day.) The value is truncated to that of the filesystem’s timestamp resolution; for example, on some FAT-based filesystems, only the date of last access is recorded, so this time will always hold the midnight of the day of the last access.
5. The time of last modification as a list of four integers (as above) (file-attribute-modification-time). This is the last time when the file’s contents were modified.
6. The time of last status change as a list of four integers (as above) (file-attribute-status-change-time). This is the time of the last change to the file’s access mode bits, its owner and group, and other information recorded in the filesystem for the file, beyond the file’s contents.
7. The size of the file in bytes (file-attribute-size). This is floating point if the size is too large to fit in a Lisp integer.
8. The file’s modes, as a string of ten letters or dashes, as in ‘ls -l’ (file-attribute-modes).
9. An unspecified value, present for backward compatibility.
10. The file’s inode number (file-attribute-inode-number). If possible, this is an integer. If the inode number is too large to be represented as an integer in Emacs Lisp but dividing it by 2^{16} yields a representable integer, then the value has the form (high . low), where low holds the low 16 bits. If the inode number is too wide for even that, the value is of the form (high middle . low), where high holds the high bits, middle the middle 24 bits, and low the low 16 bits.
11. The filesystem number of the device that the file is on file-attribute-device-number). Depending on the magnitude of the value, this can be either an integer or a cons cell, in the same manner as the inode number. This element and the file’s inode number together give enough information to distinguish any two files on the system—no two files can have the same values for both of these numbers.

For example, here are the file attributes for files.texi:

(file-attributes "files.texi" 'string)
     ⇒  (nil 1 "lh" "users"
          (20614 64019 50040 152000)
          (20000 23 0 0)
          (20614 64555 902289 872000)
          122295 "-rw-rw-rw-"
          t (5888 2 . 43978)
          (15479 . 46724))

and here is how the result is interpreted:

nil

is neither a directory nor a symbolic link.

1

has only one name (the name files.texi in the current default directory).

"lh"

is owned by the user with name ‘lh’.

"users"

is in the group with name ‘users’.

(20614 64019 50040 152000)

was last accessed on October 23, 2012, at 20:12:03.050040152 UTC.

(20000 23 0 0)

was last modified on July 15, 2001, at 08:53:43 UTC.

(20614 64555 902289 872000)

last had its status changed on October 23, 2012, at 20:20:59.902289872 UTC.

122295

is 122295 bytes long. (It may not contain 122295 characters, though, if some of the bytes belong to multibyte sequences, and also if the end-of-line format is CR-LF.)

"-rw-rw-rw-"

has a mode of read and write access for the owner, group, and world.

t

is merely a placeholder; it carries no information.

(5888 2 . 43978)

has an inode number of 6473924464520138.

(15479 . 46724)

is on the file-system device whose number is 1014478468.

Function: file-nlinks filename

This function returns the number of names (i.e., hard links) that file filename has. If the file does not exist, this function returns nil. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to. This function does not follow symbolic links.

$ ls -l foo*
-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo
-rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1

(file-nlinks "foo")
     ⇒ 2

(file-nlinks "doesnt-exist")
     ⇒ nil