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

   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 parameters are concatenated
   and  sent  to  "standard  output"  (see  stdout(3)),  here the terminal

   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 ~".

   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 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.

   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.


   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),


   This page is part of release 4.09 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


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