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INTRO(1)		   Linux Programmer's Manual		      INTRO(1)

NAME
       intro - Introduction to user commands

DESCRIPTION
       Linux  is a flavour of Unix, and	as a first approximation all user com-
       mands under Unix	work precisely the same	under Linux (and  FreeBSD  and
       lots of other Unix-like systems).

       Under  Linux  there are GUIs (graphical user interfaces), where you can
       point and click and drag, and hopefully get  work  done	without	 first
       reading	lots  of  documentation. The traditional Unix environment is a
       CLI (command line interface), where you type commands to	tell the  com-
       puter  what to do. That is faster and more powerful, but	requires find-
       ing out what the	commands are.  Below a bare minimum, to	get started.

   Login
       In order	to start working, you probably first have to login,  that  is,
       give  your username and password. See also login(1).  The program login
       now starts a shell (command interpreter)	for you.  In case of a graphi-
       cal  login, you get a screen with menus or icons	and a mouse click will
       start a shell in	a window. See also xterm(1).

   The shell
       One types commands to the shell,	the command  interpreter.  It  is  not
       built-in,  but  is just a program and you can change your shell.	Every-
       body has	her own	favourite one.	The standard one is  called  sh.   See
       also ash(1), bash(1), csh(1), zsh(1), chsh(1).

       A session might go like

	      knuth login: aeb
	      Password:	********
	      %	date
	      Tue Aug  6 23:50:44 CEST 2002
	      %	cal
		   August 2002
	      Su Mo Tu We Th Fr	Sa
			   1  2	 3
	       4  5  6	7  8  9	10
	      11 12 13 14 15 16	17
	      18 19 20 21 22 23	24
	      25 26 27 28 29 30	31

	      %	ls
	      bin  tel
	      %	ls -l
	      total 2
	      drwxrwxr-x   2 aeb       1024 Aug	 6 23:51 bin
	      -rw-rw-r--   1 aeb	 37 Aug	 6 23:52 tel
	      %	cat tel
	      maja    0501-1136285
	      peter   0136-7399214
	      %	cp tel tel2
	      %	ls -l
	      total 3
	      drwxr-xr-x   2 aeb       1024 Aug	 6 23:51 bin
	      -rw-r--r--   1 aeb	 37 Aug	 6 23:52 tel
	      -rw-r--r--   1 aeb	 37 Aug	 6 23:53 tel2
	      %	mv tel tel1
	      %	ls -l
	      total 3
	      drwxr-xr-x   2 aeb       1024 Aug	 6 23:51 bin
	      -rw-r--r--   1 aeb	 37 Aug	 6 23:52 tel1
	      -rw-r--r--   1 aeb	 37 Aug	 6 23:53 tel2
	      %	diff tel1 tel2
	      %	rm tel1
	      %	grep maja tel2
	      maja    0501-1136285
	      %
       and  here  typing Control-D ended the session.  The % here was the com-
       mand prompt - it	is the shell's way of indicating that it is ready  for
       the next	command. The prompt can	be customized in lots of ways, and one
       might include stuff like	user name, machine  name,  current  directory,
       time,  etc.   An	 assignment PS1="What next, master? " would change the
       prompt as indicated.

       We see that there are commands date (that gives date and	time), and cal
       (that givs a calendar).

       The  command  ls	lists the contents of the current directory - it tells
       you what	files you have.	With a -l option it gives a long listing, that
       includes	 the  owner and	size and date of the file, and the permissions
       people have for reading and/or changing the  file.   For	 example,  the
       file  "tel"  here is 37 bytes long, owned by aeb	and the	owner can read
       and write it, others can	only read it.  Owner and  permissions  can  be
       changed by the commands chown and chmod.

       The  command  cat  will show the	contents of a file.  (The name is from
       "concatenate and	print":	all files given	as parameters are concatenated
       and sent	to "standard output", here the terminal	screen.)

       The  command cp (from "copy") will copy a file.	On the other hand, the
       command mv (from	"move")	only renames it.

       The command diff	lists the differences between two files.   Here	 there
       was no output because there were	no differences.

       The  command rm (from "remove") deletes the file, and be	careful! it is
       gone.  No wastepaper basket or anything.	Deleted	means lost.

       The command grep	(from "g/re/p")	finds occurrences of a string  in  one
       or more files.  Here it finds Maja's telephone number.

   Path	names and the current directory
       Files  live  in a large tree, the file hierarchy.  Each has a path name
       describing the path from	the root of the	tree (which is	called	/)  to
       the  file.  For	example, such a	full path name might be	/home/aeb/tel.
       Always using full path names would be inconvenient, and the name	 of  a
       file  in	 the  current  directory may be	abbreviated by only giving the
       last component. That is why "/home/aeb/tel" can be abbreviated to "tel"
       when the	current	directory is "/home/aeb".

       The command pwd prints the current directory.

       The command cd changes the current directory.  Try "cd /" and "pwd" and
       "cd" and	"pwd".

   Directories
       The command mkdir makes a new directory.

       The command rmdir removes a directory if	it  is	empty,	and  complains
       otherwise.

       The  command  find  (with a rather baroque syntax) will find files with
       given name or other properties. For example, "find . -name  tel"	 would
       find  the file "tel" starting in	the present directory (which is	called
       ".").  And "find	/ -name	tel" would do the same,	but  starting  at  the
       root  of	 the tree. Large searches on a multi-GB	disk will be time-con-
       suming, and it may be better to use locate(1).

   Disks and Filesystems
       The command mount will attach the filesystem found  on  some  disk  (or
       floppy, or CDROM	or so) to the big filesystem hierarchy.	And umount de-
       taches it again.	 The command df	will tell you how much of your disk is
       still free.

   Processes
       On  a  Unix  system  many user and system processes run simultaneously.
       The one you are talking to runs in the foreground, the  others  in  the
       background.   The  command  ps will show	you which processes are	active
       and what	numbers	these processes	have.  The command kill	allows you  to
       get  rid	 of them. Without option this is a friendly request: please go
       away. And "kill -9" followed by the number of the process is an immedi-
       ate  kill.  Foreground processes	can often be killed by typing Control-
       C.

   Getting information
       There are thousands of commands,	each with many options.	 Traditionally
       commands	are documented on man pages, (like this	one), so that the com-
       mand "man kill" will document the use of	the command "kill"  (and  "man
       man"  document  the  command  "man").   The  program man	sends the text
       through some pager, usually less.  Hit the space	bar to	get  the  next
       page, hit q to quit.

       In  documentation  it  is custumary to refer to man pages by giving the
       name and	section	number,	as in man(1).  Man pages are terse, and	 allow
       you  to	find quickly some forgotten detail. For	newcomers an introduc-
       tory text with more examples and	explanations is	useful.

       A lot of	GNU/FSF	software is provided with info files. Type "info info"
       for an introduction on the use of the program "info".

       Special	  topics    are	   often    treated   in   HOWTOs.   Look   in
       /usr/share/doc/howto/en and use a browser if you	find HTML files	there.

Linux				  2002-08-06			      INTRO(1)

NAME | DESCRIPTION

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