Ls

In computing,   is a command to list computer files and directories in Unix and Unix-like operating systems. It is specified by POSIX and the Single UNIX Specification. It is available in the EFI shell, as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities, or as part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.

The numerical computing environments MATLAB and GNU Octave include an  function with similar functionality.

In other environments, such as DOS, OS/2, and Microsoft Windows, similar functionality is provided by the  command.

History
An  utility appeared in the first version of AT&T UNIX, the name inherited from a similar command in Multics also named 'ls', short for the word "list". ls is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX.1 and the Single Unix Specification.

Behavior
Unix and Unix-like operating systems maintain the idea of a working directory. When invoked without arguments,  lists the files in the working directory. If a directory is specified as an argument, the files in that directory are listed; if a file is specified, that file is listed. Multiple directories and files may be specified.

In many Unix-like systems, names starting with a dot are hidden. Examples are, which refers to the working directory, and  , which refers to its parent directory. Hidden names are not shown by default. With, all names, including all hidden names, are shown. Using  shows all names, including hidden names, except for   and. File names specified explicitly (for example ) are always listed.

Without options,  displays names only. The different implementations have different options, but common options include:
 * Long format, displaying Unix file types, permissions, number of hard links, owner, group, size, last-modified date-time and name. If the modified date is older than 6 months, the time is replaced with the year. Some implementations add additional flags to permissions. The file type can be one of 8 characters:, regular file;  , directory;  , symbolic (soft) link;  , network files;  , socket;  , named pipe (FIFO);  , character special file;  , block special file.
 * Output sizes in human readable format (e.g., 1K (kilobytes), 234M (megabytes), 2G (gigabytes)). This option is not part of the POSIX standard, although implemented in several systems, e.g., GNU coreutils in 1997, FreeBSD 4.5 in 2002, and Solaris 9 in 2002.

Additional options controlling how items are displayed include:
 * Recursively list items in subdirectories.
 * Sort the list by modification time (default sort is alphabetically).
 * Sort the list by last access time.
 * Sort the list by last attribute (status) change time.
 * Reverse the order, for example most recent time last.
 * Show times down to the second and millisecond instead of just the minute.
 * One entry per line.
 * Stream format; list items across the page, separated by commas.
 * Include group but not owner.
 * Include owner but not group (when combined with  both group and owner are suppressed).
 * Show information about a directory or symbolic link, rather than the contents of a directory or the link's target.
 * Append a "/" to directory names and a "*" to executable files.

It may be possible to highlight different types of items with different colors. This is an area where implementations differ: When the option to use color to indicate item types is selected, the output might look like:
 * GNU  uses the   option; it checks the Unix file type, the file permissions and the file extension and uses its own database to control colors maintained using dircolors.
 * FreeBSD  uses the   option; it checks only the Unix file type and file permissions and uses the termcap database

-rw-r--r--   1 tsmitt nregion   26650 Dec 20 11:16 audio.ogg brw-r--r--   1 tsmitt nregion      64 Jan 27 05:52 bd-block-device crw-r--r--   1 tsmitt nregion     255 Jan 26 13:57 cd-character-device -rw-r--r--   1 tsmitt nregion     290 Jan 26 14:08 image.png drwxrwxr-x   2 tsmitt nregion      48 Jan 26 11:28 di-directory -rwxrwxr-x   1 tsmitt nregion      29 Jan 26 14:03 ex-executable -rw-r--r--   1 tsmitt nregion       0 Dec 20 09:39 fi-regular-file lrwxrwxrwx   1 tsmitt nregion       3 Jan 26 11:44 ln-soft-link -> dir lrwxrwxrwx   1 tsmitt nregion      15 Dec 20 10:57 or-orphan-link -> mi-missing-link drwxr-xrwx   2 tsmitt nregion    4096 Dec 20 10:58 ow-other-writeable-dir prw-r--r--   1 tsmitt nregion       0 Jan 26 11:50 pi-pipe -rwxr-sr-x   1 tsmitt nregion       0 Dec 20 11:05 sg-setgid srw-rw-rw-   1 tsmitt nregion       0 Jan 26 12:00 so-socket drwxr-xr-t   2 tsmitt nregion    4096 Dec 20 10:58 st-sticky-dir -rwsr-xr-x   1 tsmitt nregion       0 Dec 20 11:09 su-setuid -rw-r--r--   1 tsmitt nregion   10240 Dec 20 11:12 compressed.gz  drwxrwxrwt    2 tsmitt nregion    4096 Dec 20 11:10 tw-sticky-other-writeable-dir

Sample usage
The following example demonstrates the output of the command: Each line shows the  (directory) or   (file) indicator, Unix file permission notation, number of hard links (1 or 3), the file's owner, the file's group, the file size, the modification date/time, and the file name. In the working directory, the owner  has a directory named , a regular file named  , and an executable named   which is "old", i.e. modified more than 6 months ago as indicated by the display of the year.