Howto: Understand Output From ls

When you type in ls -la, you might get something like this:

~/stuff fergie$ ls -l
total 6584
-rw-r--r--    1 fergie  fergie  1252146 Jan 28 19:51 009.jpg
-rw-r--r--    1 fergie  fergie  1251616 Jan 28 19:50 Adam.jpg
-rw-r--r--    1 fergie  fergie    13587 Jan 30 20:04 BUN103-DXHZ.pdf
-rw-r--r--    1 fergie  fergie   141821 Apr 17 09:53 Ryanair_flight_19_04_2007.pdf
-rw-r--r--    1 fergie  wheel    114710 Feb 14 20:12 glasgow.pdf
drwxr-xr-x   73 fergie  fergie     2482 Jan 28 19:40 linnea_jan_07
-rw-r--r--    1 fergie  fergie   583168 Jan 25 21:29 presentation.pps

So what does all that stuff actually mean? Well the format of ls -l output is as follows: file mode, number of links, owner name, group name, item size (in bytes by default), month of last modification, day of last modification, time of last modification, name. So for example the first entry can be interpreted as follows.

file mode:	-rw-r--r--
number of links:	1
owner name:	fergie
group name:	fergie
item size:	1252146 bytes
month of last modification	January
day of last modification	28th
time of last modification	19:51
name:	009.jpg

Howto: Display Directory Contents Using ls

Use ls to display the contents of a directory:

~ fergie$ ls
Desktop                 Movies                  Pictures
Documents               Music                   Public
Library                 Opera 7 Preferences.new Sites

Use the -l flag by typing ls -l to get more details on the files and directories:

~ fergie$ ls -l 
total 0
drwx------    26 fergie  fergie   884 May 28 12:02 Desktop
drwx------     4 fergie  fergie   136 Feb  1 15:54 Documents
drwx------    29 fergie  fergie   986 Feb  1 16:19 Library
drwx------     3 fergie  fergie   102 Dec 20 18:20 Movies
drwx------     3 fergie  fergie   102 Dec 20 18:20 Music
-rw-r--r--     1 root    fergie     0 Feb  1 16:01 Opera 7 Preferences.new
drwx------   185 fergie  fergie  6290 Feb 27 15:35 Pictures
drwxr-xr-x     5 fergie  fergie   170 Feb 27 10:42 Public
drwxr-xr-x     5 fergie  fergie   170 Dec 20 18:20 Sites

Add the -a flag by typing ls -la to show 'hidden' items generally, but not exclusively, used to store configuration information. Hidden items are prefixed with a period- for example .Trash:

~ fergie$ ls -la
total 40
drwxr-xr-x    17 fergie  fergie   578 Feb  6 15:45 .
drwxrwxr-t     7 root    admin    238 Jan 31 17:21 ..
-rw-r--r--     1 fergie  fergie     3 Dec 20 18:20 .CFUserTextEncoding
-rw-r--r--     1 fergie  fergie  6148 Feb 27 17:30 .DS_Store
drwx------    28 fergie  fergie   952 May 24 17:09 .Trash
-rw-------     1 fergie  fergie  1252 May 28 11:48 .bash_history
-rw-r--r--     1 fergie  fergie    13 Feb  6 15:45 .lpoptions
drwx------     3 fergie  fergie   102 Dec 20 20:18 .ssh
drwx------    26 fergie  fergie   884 May 28 12:02 Desktop
drwx------     4 fergie  fergie   136 Feb  1 15:54 Documents
drwx------    29 fergie  fergie   986 Feb  1 16:19 Library
drwx------     3 fergie  fergie   102 Dec 20 18:20 Movies
drwx------     3 fergie  fergie   102 Dec 20 18:20 Music
-rw-r--r--     1 root    fergie     0 Feb  1 16:01 Opera 7 Preferences.new
drwx------   185 fergie  fergie  6290 Feb 27 15:35 Pictures
drwxr-xr-x     5 fergie  fergie   170 Feb 27 10:42 Public
drwxr-xr-x     5 fergie  fergie   170 Dec 20 18:20 Sites

To order by time of most recent update add the -t flag:

~ fergie$ ls -lat
total 40
drwx------    26 fergie  fergie   884 May 28 12:02 Desktop
-rw-------     1 fergie  fergie  1252 May 28 11:48 .bash_history
drwx------    28 fergie  fergie   952 May 24 17:09 .Trash
-rw-r--r--     1 fergie  fergie  6148 Feb 27 17:30 .DS_Store
drwx------   185 fergie  fergie  6290 Feb 27 15:35 Pictures
drwxr-xr-x     5 fergie  fergie   170 Feb 27 10:42 Public
drwxr-xr-x    17 fergie  fergie   578 Feb  6 15:45 .
-rw-r--r--     1 fergie  fergie    13 Feb  6 15:45 .lpoptions
drwx------    29 fergie  fergie   986 Feb  1 16:19 Library
-rw-r--r--     1 root    fergie     0 Feb  1 16:01 Opera 7 Preferences.new
drwx------     4 fergie  fergie   136 Feb  1 15:54 Documents
drwxrwxr-t     7 root    admin    238 Jan 31 17:21 ..
drwx------     3 fergie  fergie   102 Dec 20 20:18 .ssh
-rw-r--r--     1 fergie  fergie     3 Dec 20 18:20 .CFUserTextEncoding
drwx------     3 fergie  fergie   102 Dec 20 18:20 Movies
drwx------     3 fergie  fergie   102 Dec 20 18:20 Music
drwxr-xr-x     5 fergie  fergie   170 Dec 20 18:20 Sites

The -r flag reverses the order of any sorting, so adding it to the previous example would return a cronologically ordered list with the oldest item first:

~ fergie$ ls -latr
total 40
drwxr-xr-x     5 fergie  fergie   170 Dec 20 18:20 Sites
drwx------     3 fergie  fergie   102 Dec 20 18:20 Music
drwx------     3 fergie  fergie   102 Dec 20 18:20 Movies
-rw-r--r--     1 fergie  fergie     3 Dec 20 18:20 .CFUserTextEncoding
drwx------     3 fergie  fergie   102 Dec 20 20:18 .ssh
drwxrwxr-t     7 root    admin    238 Jan 31 17:21 ..
drwx------     4 fergie  fergie   136 Feb  1 15:54 Documents
-rw-r--r--     1 root    fergie     0 Feb  1 16:01 Opera 7 Preferences.new
drwx------    29 fergie  fergie   986 Feb  1 16:19 Library
-rw-r--r--     1 fergie  fergie    13 Feb  6 15:45 .lpoptions
drwxr-xr-x    17 fergie  fergie   578 Feb  6 15:45 .
drwxr-xr-x     5 fergie  fergie   170 Feb 27 10:42 Public
drwx------   185 fergie  fergie  6290 Feb 27 15:35 Pictures
-rw-r--r--     1 fergie  fergie  6148 Feb 27 17:30 .DS_Store
drwx------    28 fergie  fergie   952 May 24 17:09 .Trash
-rw-------     1 fergie  fergie  1252 May 28 11:48 .bash_history
drwx------    26 fergie  fergie   884 May 28 12:02 Desktop

-S (capitalised) sorts by size:

~ fergie$ ls -laS 
total 40
drwx------   185 fergie  fergie  6290 Feb 27 15:35 Pictures
-rw-r--r--     1 fergie  fergie  6148 Feb 27 17:30 .DS_Store
-rw-------     1 fergie  fergie  1252 May 28 11:48 .bash_history
drwx------    29 fergie  fergie   986 Feb  1 16:19 Library
drwx------    28 fergie  fergie   952 May 24 17:09 .Trash
drwx------    26 fergie  fergie   884 May 28 12:02 Desktop
drwxr-xr-x    17 fergie  fergie   578 Feb  6 15:45 .
drwxrwxr-t     7 root    admin    238 Jan 31 17:21 ..
drwxr-xr-x     5 fergie  fergie   170 Feb 27 10:42 Public
drwxr-xr-x     5 fergie  fergie   170 Dec 20 18:20 Sites
drwx------     4 fergie  fergie   136 Feb  1 15:54 Documents
drwx------     3 fergie  fergie   102 Dec 20 20:18 .ssh
drwx------     3 fergie  fergie   102 Dec 20 18:20 Movies
drwx------     3 fergie  fergie   102 Dec 20 18:20 Music
-rw-r--r--     1 fergie  fergie    13 Feb  6 15:45 .lpoptions
-rw-r--r--     1 fergie  fergie     3 Dec 20 18:20 .CFUserTextEncoding
-rw-r--r--     1 root    fergie     0 Feb  1 16:01 Opera 7 Preferences.new

...and -h makes those sizes human readable:

~ fergie$ ls -laSh
total 40
drwx------   185 fergie  fergie    6K Feb 27 15:35 Pictures
-rw-r--r--     1 fergie  fergie    6K Feb 27 17:30 .DS_Store
-rw-------     1 fergie  fergie    1K May 28 11:48 .bash_history
drwx------    29 fergie  fergie  986B Feb  1 16:19 Library
drwx------    28 fergie  fergie  952B May 24 17:09 .Trash
drwx------    26 fergie  fergie  884B May 28 12:02 Desktop
drwxr-xr-x    17 fergie  fergie  578B Feb  6 15:45 .
drwxrwxr-t     7 root    admin   238B Jan 31 17:21 ..
drwxr-xr-x     5 fergie  fergie  170B Feb 27 10:42 Public
drwxr-xr-x     5 fergie  fergie  170B Dec 20 18:20 Sites
drwx------     4 fergie  fergie  136B Feb  1 15:54 Documents
drwx------     3 fergie  fergie  102B Dec 20 20:18 .ssh
drwx------     3 fergie  fergie  102B Dec 20 18:20 Movies
drwx------     3 fergie  fergie  102B Dec 20 18:20 Music
-rw-r--r--     1 fergie  fergie   13B Feb  6 15:45 .lpoptions
-rw-r--r--     1 fergie  fergie    3B Dec 20 18:20 .CFUserTextEncoding
-rw-r--r--     1 root    fergie    0B Feb  1 16:01 Opera 7 Preferences.new

Technorati tags:bash, unix, linux, osx

Howto: Move Around Using cd

Use the cd (change directory) command to navigate through directories.

Using the shell

The shell is the window where you type in commands. The unix shell is conceptually synonymous with the Windows 'command-line' although the commands are different. Most flavours of unix use bash, so this reference is intended to be bash-specific.

To find out what shell you are using type the following:

>echo $0

You could also type in:

>echo $SHELL

But this would only give you the default shell. If for some reason you had changed shell since logging in, echo $SHELL would not give you the current shell.

The terminal will now display a path which ends in either /sh, /csh, /tcsh, /ksh or /bash.

You can change shell by typing in 'sh', 'csh', 'tcsh', 'ksh' or 'bash'. Note that you are not strictly speaking changing shells but spawning new shells on top of the existing ones. To get back to the previous shell, use the 'exit' shortcut (ctrl-d) or type exit.

For the purposes of this manual echo $0 should return a path which ends in /bash, meaning that you are working in a bash shell. If for some reason you are not, type in bash which will invoke the bash shell.

Now we need to look at some commands!

What is Unix?

Unix is more widespread than you might think. Unix is a catch-all term that can describe a family of operating systems including Linux, BSD, Solaris, AIX and MacOSX (which is the operating system that runs on every Mac). In other words, these days, we can pretty much say that any desktop computer that is not running windows is running a form of unix. Clearly most desktop computers run windows, however most servers run Unix.