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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.

       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 com‐
       mand 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 tradi‐
       tional 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  inter‐
       preter) 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 stan‐
       dard 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 cus‐
       tomized 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 cal‐

       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  wastepa‐
       per 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 path‐
       name 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 compo‐
       nent.  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-consum‐
       ing, 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 talk‐
       ing 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 pro‐
       cesses can often be killed by typing Control-C.

   Getting information
       There are thousands of commands, each with many options.  Traditionally commands are docu‐
       mented 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 num‐
       ber,  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  introduc‐
       tion 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.


       This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.

Linux                                       2007-11-15                                   INTRO(1)

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