intro



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 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 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-
       consuming, 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
       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 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)

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