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



NAME
       intro - Introduction to user commands

DESCRIPTION
       Section 1 of the manual describes user commands and tools, for example, file manip-
       ulation tools, shells, compilers, 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 conven-
       tionally 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 failed.

NOTES
       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  documen-
       tation.   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  power-
       ful,  but requires finding 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 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 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 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  permis-
       sions 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.

   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".

   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" start-
       ing  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 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
       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  sec-
       tion 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 expla-
       nations 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.

SEE ALSO
       standards(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2007-11-15                          INTRO(1)

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