ls

A long file listing with "ls -l" in OpenBSD 5.3

In computing, ls is a command to list computer files in Unix and Unix-like operating systems. ls is specified by POSIX and the Single UNIX Specification. When invoked without any arguments, ls lists the files in the current working directory. The command is also available in the EFI shell.[1] In other environments, such as DOS and Microsoft Windows, similar functionality is provided by the dir command.

History

An ls utility appeared in the original version of AT&T UNIX, the name inherited from a similar command in Multics also named 'ls', short for the word "list".[2][3][4]

Today, the two popular versions of ls are the one provided with the GNU coreutils package, and that released by various BSD variants. Both are free software and open source, and have only minor syntax differences.

Behavior

Unix and Unix-like operating systems maintain the idea of a current working directory, that is, where one is currently positioned in the hierarchy of directories. When invoked without any arguments, ls lists the files in the current working directory. If another directory is specified, then ls will list the files there, and in fact the user may specify any list of files and directories to be listed.

Files whose names start with "." are not listed, unless the -a flag is specified, the -A flag is specified, or the files are specified explicitly.

Without options, ls displays files in a bare format. This bare format however makes it difficult to establish the type, permissions, and size of the files. The most common options to reveal this information or change the list of files are:

  • -l long format, displaying Unix file types, permissions, number of hard links, owner, group, size, last-modified date and filename
  • -f do not sort. Useful for directories containing large numbers of files.
  • -F appends a character revealing the nature of a file, for example, * for an executable, or / for a directory. Regular files have no suffix.
  • -a lists all files in the given directory, including those whose names start with "." (which are hidden files in Unix). By default, these files are excluded from the list.
  • -R recursively lists subdirectories. The command ls -R / would therefore list all files.
  • -d shows information about a symbolic link or directory, rather than about the link's target or listing the contents of a directory.
  • -t sort the list of files by modification time.
  • -h print sizes in human readable format. (e.g., 1K, 234M, 2G, etc.) This option is not part of the POSIX standard, although implemented in several systems, e.g., GNU coreutils in 1997,[5] FreeBSD 4.5 in 2002,[6] and Solaris 9 in 2002.[7]

It's normally possible to highlight different types of files with different colors, instead of with characters as -F would, but this is an area where the two main ls versions differ:

  • GNU ls uses the --color option; checks the Unix file type, the file permissions, and the file extension; and uses its own database to control colors.[8]
  • FreeBSD ls uses the or -G option; checks only the Unix file type and file permissions. and uses the termcap database[9]

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

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

Sample usage

The following example demonstrates the output of the ls command given two different arguments (pwd is a command that shows the present working directory, or in other words, the folder you are currently in):

$ pwd
/home/fred
$ ls -l
drwxr--r--   1 fred  editors   4096  drafts
-rw-r--r--   1 fred  editors  30405  edition-32
-r-xr-xr-x   1 fred  fred      8460  edit
$ ls -F
drafts/
edition-32
edit*

In this example, the user fred has a directory named drafts, a regular file called edition-32, and an executable named edit in his home directory. ls uses Unix file permission notation to indicate which users or groups are allowed to access each file or directory.

drwxr--r--   1 fred  editors   4096  Mar 1  2007 drafts

In this example, drafts is a directory (denoted by the file descriptor d), and the characters after this indicate the permissions:

  • rwx: the owner (fred) has the right to read (r), write (w) and execute (x)
  • r--: group members (users part of the editors group) have read-only permissions; write and execute are not permitted, as denoted by the hyphen characters (-)
  • r--: others (users aside from the owner or members of editors) have read-only permissions; write and execute are not permitted

See also

Notes

  1. ↑ "EFI Shells and Scripting". Intel. Retrieved 2013-09-25.
  2. ↑ Multics manual page for ls or list command
  3. ↑ "A Brief History of the 'ls' command", Eric Fischer, The Linux Documentation Project
  4. ↑ "Multics programmer's manual - Commands and active functions" (PDF). p. 397.
  5. ↑ "(decode_switches): -h and -H override output units". coreutils.git. 1997-12-31.
  6. ↑ "[base] Log of /stable/10/bin/ls/ls.c". 2001-12-28.
  7. ↑ What's New in the Solaris 9 Operating Environment, Sun Microsystems, 2002
  8. ↑ "NCURSES — Frequently Asked Questions (FAQ): My terminal doesn't recognize color". Retrieved June 23, 2013.
  9. ↑ "FreeBSD Man Pages — ls". Retrieved June 23, 2013.
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