ls

An ls 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".^[6][7][8] 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.^[9]

Unix and Unix-like operating systems maintain the idea of a working directory. When invoked without arguments, ls 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 -a, all names, including all hidden names, are shown. Using -A shows all names, including hidden names, except for . and ... File names specified explicitly (for example ls .secret) are always listed.

Without options, ls displays names only. The different implementations have different options, but common options include:

• -l 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; d, directory; l, symbolic (soft) link; n, network files; s, socket; p, named pipe (FIFO); c, character special file; b, block special file.
• -h 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,^[10] FreeBSD 4.5 in 2002,^[11] and Solaris 9 in 2002.^[12]

Additional options controlling how items are displayed include:

• -R Recursively list items in subdirectories.
• -t Sort the list by modification time (default sort is alphabetically).
• -u Sort the list by last access time.
• -c Sort the list by last attribute (status) change time.
• -r Reverse the order, for example most recent time last.
• --full-time Show times down to the second and millisecond instead of just the minute.
• -1 One entry per line.
• -m Stream format; list items across the page, separated by commas.
• -g Include group but not owner.
• -o Include owner but not group (when combined with -g both group and owner are suppressed).
• -d Show information about a directory or symbolic link, rather than the contents of a directory or the link's target.
• -F 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:

• GNU ls uses the --color option;^[13] 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 ls uses the -G option; it checks only the Unix file type and file permissions and uses the termcap database^[14]

When the option to use color to indicate item types is selected, the output might look like:

-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

The following example demonstrates the output of the command:

$ ls -l
drwxr--r--   1 fjones editors     4096 Mar  2 12:52  drafts
-rw-r--r--   3 fjones editors    30405 Mar  2 12:52  edition-32
-r-xr-xr-x   1 fjones bookkeepers 8460 Jan 16  2022  edit.sh

Each line shows the d (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 fjones has a directory named drafts, a regular file named edition-32, and an executable named edit.sh which is "old", i.e. modified more than 6 months ago as indicated by the display of the year.

┌─────────── file (not a directory)
|┌─────────── read-write (no execution) permissions for the owner
|│  ┌───────── read-only permissions for the group
|│  │  ┌─────── read-only permissions for others
|│  │  │     ┌── number of hard links
|│  │  │     │   ┌── owner
|│  │  │     │   │     ┌── user group
|│  │  │     │   │     │          ┌── file size in bytes
|│  │  │     │   │     │          │    ┌── last modified on
|│  │  │     │   │     │          │    │                ┌── filename
-rw-r--r--   3 fjones editors    30405 Mar  2 12:52  edition-32

• stat (Unix)
• chown
• chgrp
• du (Unix)
• mdls
• User identifier (Unix)
• Group identifier (Unix)
• List of Unix commands
• Unix directory structure

 

The Wikibook Guide to Unix has a page on the topic of: Commands

• ls – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
• ls(1) – FreeBSD General Commands Manual
• ls(1) – NetBSD General Commands Manual
• ls(1) – OpenBSD General Commands Manual
• ls(1) – Solaris 11.4 User Commands Reference Manual
• ls(1) – Linux User Manual – User Commands
• ls(1) – Plan 9 Programmer's Manual, Volume 1
• ls(1) – Inferno General commands Manual
• GNU ls source code (as part of coreutils)
• ls at the LinuxQuestions.org wiki