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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, 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 conventionally used to indicate
       success, and a nonzero status means that the command was unsuccessful.
       (Details of the exit status can be found in wait(2).)  A nonzero exit
       status can be in the range 1 to 255, and some commands use different
       nonzero status values to indicate the reason why the command failed.

       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

       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 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 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.

   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

       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 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.

       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

   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 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 3.25 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at

Linux                             2007-11-15                          INTRO(1)


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