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       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.




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