====== UNIX Tutorial Six ======
 


===== Other useful UNIX commands =====

==== quota ====

If you have a student's login account on a shared Linux system, it is
likely that you will have been allocated a certain amount of disk
space on the file system for your personal files. If you go over your
quota, you are given 7 days to remove excess files.

To check your current quota and how much of it you have used, type 
<cli>ubuntu@ubuntu:~/unixstuff$ quota -v </cli>

<note>This command is not provided on Live CD version of Ubuntu (or
indeed an installed version) since you essentially own the whole
system. To install ''quota'' type ''**sudo apt-get install quota**'' from the
command line. Ubuntu will download the ''quota'' package from the internet
and install it into the system. The ''quota'' command should now be avalable.</note>  


==== df ====

The ''df'' command reports on the space left on the file
system. For example, to find out how much space is left on the
file system containing your **unixstuff** directory, type:
<cli>ubuntu@ubuntu:~/unixstuff$ df . </cli>

==== du ==== 

The ''du'' command outputs the number of kilobyes used by
each subdirectory. Useful if you have gone over quota and you want to
find out which directory has the most files. In your home-directory,
type
<cli>ubuntu@ubuntu:~$ du </cli>



==== gzip ====

This reduces the size of a file, thus freeing valuable disk space. For example, type 
<cli>ubuntu@ubuntu:~/unixtut$ ls -l science.txt</cli> 
and note the size of the file using ''ls -l''. Then to compress **science.txt**, type 
<cli>ubuntu@ubuntu:~/unixtut$ gzip science.txt</cli>
This will compress the file and place it in a file called **science.txt.gz**. 

To see the change in size, type ''ls -l'' again. 

To expand the file, use the ''gunzip'' command. 
<cli>ubuntu@ubuntu:~/unixtut$ gunzip science.txt.gz</cli>






==== zcat ====

''zcat'' will read gzipped files without needing to uncompress them first.

<cli>ubuntu@ubuntu:~$ zcat science.txt.gz</cli>

If the text scrolls too fast for you, pipe the output though ''less''. 
<cli>ubuntu@ubuntu:~$ zcat science.txt.gz | less</cli>


==== file ====

''file'' classifies the named files according to the type of data they
contain, for example ascii (text), pictures, compressed data, etc. To
report on all files in your home directory, type

<cli>ubuntu@ubuntu:~$ file * </cli>


==== diff ====

This command compares the contents of two files and displays the differences. Suppose you have a file called **file1** and you edit some part of it and save it as **file2**. To see the differences type
<cli>ubuntu@ubuntu:~$ diff file1 file2</cli> 

Lines beginning with a ''<'' denotes **file1**, while lines beginning with a ''>'' denotes **file2**. 

==== find ====

This searches through the directories for files and directories with a given name, date, size, or any other attribute you care to specify. It is a simple command but with many options -- you can read the manual by typing ''man find''. 

To search for all fies with the extention ''.txt'', starting at the current directory (''.'') and working through all sub-directories, then printing the name of the file to the screen, type
<cli>ubuntu@ubuntu:~$ find . -name "*.txt" -print</cli>

To find files over 1Mb in size, and display the result as a long listing, type
<cli>ubuntu@ubuntu:~$ find . -size +1M -ls </cli>


==== history ====

The bash shell keeps an ordered list of all the commands that you have entered. Each command is given a number according to the order it was entered.

<cli>ubuntu@ubuntu:~/unixstuff$ history # show command history list</cli>

If you are using the bash shell, you can use the exclamation character
(!) to recall commands easily.

<cli>ubuntu@ubuntu:~/unixstuff$ !! # recall last command
ubuntu@ubuntu:~/unixstuff$ !-3 # recall third most recent command 
ubuntu@ubuntu:~/unixstuff$ !5 # recall 5th command in list
ubuntu@ubuntu:~/unixstuff$ !grep # recall last command starting with grep</cli>

You can set the size of the history buffer (default is 500) by typing
<cli>ubuntu@ubuntu:~/unixstuff$ HISTSIZE=100 </cli>





===== Summary ===== 

^ **Command**                     ^ **Meaning**                                                     ^
| ''quota''                       | display user's file quota                                       |
| ''df''                          | reports available space on the file system                     |  
| ''du''                          | show disk space used by file system                             |
| ''gzip''/''gunzip''             | compress (zip)/uncompress (unizip) a file                       | 
| ''sudo //task//''               | run a task as "super user" (i.e. with administrator privileges) |
| ''apt-get install //package//'' | (download and) install the package **package**                  |
| ''file'' //file//               | attempt to classify a file according to its contents            |
| ''zcat'' //file.gz//            | list the contents of a gzipped file without unzipping it        |
| ''find'' [//options//]          | find files according to a large number of attributes            |
| ''diff''                        | compare two (text) files and print the differences              |
| ''history''                     | show the history of commands entered into the shell             |

----

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 --- //[[C.P.Jobling@Swansea.ac.uk|Dr Chris P. Jobling]] 2007/09/21 17:39//