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

       intro - Introduction to user commands

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

       All commands yield a status value on termination.  This value can be tested (e.g., in most shells the  variable
       $?   contains  the  status  of the last executed command) to see whether the command completed successfully.  A
       zero exit status is conventionally used to indicate success, and a non-zero status means that the  command  was
       unsuccessful.   (Details  of  the  exit  status can be found in wait(2).)  A non-zero exit status can be in the
       range 1 to 255, and some commands use different non-zero status values to indicate the reason why  the  command

       Linux  is  a  flavor of Unix, and as a first approximation all user commands 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 computer what to do.  That is faster  and  more  powerful,
       but requires finding out what the commands are.  Below a bare minimum, to get started.

       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  graphical
       login,  you  get  a  screen  with  menus  or  icons and a mouse click will start a shell in a window.  See also

   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.  Everybody has her own favorite 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 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, 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 peo-
       ple 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 com-
       mands 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

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

       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 pathnames 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".

       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 exam-
       ple, "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 file system found on some disk (or floppy, or CDROM or so) to the big file
       system hierarchy.  And umount detaches it again.  The command df will tell you how much of your disk  is  still

       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  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" doc-
       ument  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
       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.


       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at

Linux                             2007-11-15                          INTRO(1)