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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 started.

       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, 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

       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 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 "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 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.

       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 Control-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 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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