intro(1)



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 manipulation tools, shells,  compilers,  web  browsers,  file  and
       image viewers and editors, and so on.

NOTES
       Linux  is  a flavor 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 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.  Every-
       body 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, mas-
       ter? " 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  permis-
       sions  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"  (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 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  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 ~".

   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 imme-
       diate kill.  Foreground processes can often be killed  by  typing  Con-
       trol-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 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  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.

SEE ALSO
       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),  stan-
       dards(7)

COLOPHON
       This  page  is  part of release 4.13 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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