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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.

       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 open a session by giving your username and password.   The  program
       login(1)  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), chsh(1),
       csh(1), dash(1), ksh(1), zsh(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

       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 parame-
       ters 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 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 num-

   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 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 ~".

       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 hierar-
       chy.  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

       Special  topics  are  often  treated in HOWTOs.  Look in /usr/share/doc/howto/en and use a browser if you find HTML files

       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)

       This  page  is  part  of  release  4.16  of the Linux man-pages project.  A description of the project, information about
       reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux                                                      2015-07-23                                                   INTRO(1)

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