The Unix ls command

The ls command displays a list of files. There are several forms of the ls command

ls

Lists the files in the current directory.

ls filename

If filename is an ordinary file, then ls simply prints out the filename again. This is rather useless: 

   linux1% ls joke2
   joke2

On the other hand, if filename is a directory, then ls will display the contents of the directory. This is much more useful: 

   linux1% ls cs104
   hw01  hw02  hw03

ls filename1 filename2 filename3 ...

Several filenames can be specified in a single ls command. This is useful in conjunction with wildcards. For example, in the following, the first ls command displays all the files in the current directory and the second ls command command displays just the C programs in the current directory: 

   linux1% ls
   a.out  hello2.c  hello3.c  hello7.c  hello.c  hello.o  inch.c typescript

   linux1% ls *.c
   hello2.c  hello3.c  hello7.c  hello.c  inch.c

If each of filename1 filename2 filename3 ... is a directory, then the files in each directory are displayed, like so: 

   linux1% ls hw01 hw02 hw03
   hw01:
   joke1  joke2  joke3

   hw02:
   bar  foo

   hw03:
   hello.c  inch.c  myhello.c

ls -a

The -a option tells ls to display all files, even ones whose filenames begin with a dot. (Those files are otherwise hidden.) The -a option can be used with the different forms of the ls command listed above. 

   linux1% ls -a
   .  ..  hw01  hw02  hw03

ls -l

The -l option tells ls to display extra information about each file. This is the "long" form of the ls command: 

   drwx------  5 chang faculty 2048 Sep  8 13:58 cs104
   -rw-------  1 chang faculty   60 Sep  8 13:28 joke2
   drwx------  2 chang faculty 2048 Sep  8 12:57 Mail
   drwx------ 33 chang faculty 2048 Sep  8 12:57 OtherStuff
   -rw-r--r--  1 chang faculty 1980 Sep  8 15:47 typescript
   lrwxr-xr-x  1 chang games     10 Sep  8 13:38 www -> ../pub/www

In the example above, cs104, Mail and OtherStuff are directories, so their listings begins with the character 'd'. The www file is a symbolic link to ../pub/www, so its listing begins with an 'l'. (Symbolic links are known as 'shortcuts' in Microsoft Windows and as 'aliases' in MacOS.) The -l option can be used with the different forms of the ls command listed above.

ls -F

The -F option adds a character to the end of the displayed filename when the file is not an ordinary file. Directories are displayed with a blackslash '/' and symbolic links are displayed with an '@'. 

   linux1% ls -F
   cs104/  joke2  Mail/  OtherStuff/  typescript  www@

The -F option is especially useful to distinguish directories and ordinary files. If you want to have ls use -F by default, you can use a shell alias: 

   linux1% ls
   cs104  joke2  Mail  OtherStuff  typescript  www

   linux1% alias ls "ls -F"

   linux1% ls
   cs104/  joke2  Mail/  OtherStuff/  typescript  www@

To revert to the original behavior, use unalias. 

   linux1% ls
   cs104/  joke2  Mail/  OtherStuff/  typescript  www@

   linux1% unalias ls

   linux1% ls
   cs104  joke2  Mail  OtherStuff  typescript  www