Manual: intro

intro(1)					   General Commands Manual					    intro(1)

NAME
       intro - introduction to user commands

DESCRIPTION
       Section	1  of the manual describes user commands and tools, for example, file manipulation tools, shells, compilers,
       web browsers, file and image viewers and editors, and so on.

NOTES
       Linux is a flavor of UNIX, and user commands under UNIX work similarly under Linux (and lots of other UNIX-like	sys‐
       tems too, like FreeBSD).

       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	 in‐
       terface),  where	 you  type commands to tell the computer what to do.  This is faster and more powerful, but requires
       finding out what the commands are and how to use them.  Below is a bare minimum guide to get you started.

   Login
       In order to start working, you'll probably first have to open a session.	 The program login(1) will wait for  you  to
       type  your  username and password, and after that, it will start a shell (command interpreter) for you.	In case of a
       graphical 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 into the shell, the command interpreter.  It is not built-in; it is just another program.  You can
       change  your  shell,  and  everybody  has  their	 own favorite one.  The standard one is called sh.  See also ash(1),
       bash(1), chsh(1), csh(1), dash(1), ksh(1), zsh(1).

       A session might look like this:

	   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
	   $

       Here typing Control-D ended the session.

       The $ here was the command 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 username, machine name, current directory,
       time, and so on.	 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 gives 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	 pa‐
       rameters are concatenated and sent to "standard output" (see stdout(3)), here the terminal screen.)

       The command cp (from "copy") will copy a file.

       The command mv (from "move"), on the other hand, only renames it.

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

       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.

   Pathnames and the current directory
       Files live in a large tree, the file hierarchy.	Each has a pathname describing the path from the root  of  the	tree
       (which  is called /) to the file.  For example, such a full pathname 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  giving  only	 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 alternatively cd and pwd commands and explore cd usage: "cd", "cd .", "cd ..", "cd /", and "cd ~".

   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-consum‐
       ing, 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 hi‐
       erarchy.	 And umount detaches 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 fore‐
       ground, 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 immediate 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 command "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  customary  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 introductory 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 pro‐
       gram 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.

SEE ALSO
       ash(1), bash(1), chsh(1), csh(1), dash(1), ksh(1), locate(1), login(1), man(1), xterm(1), zsh(1), wait(2), stdout(3),
       man-pages(7), standards(7)

Linux man-pages 6.17					 2026-02-08						    intro(1)