1INTRO(1)                      Linux User's Manual                     INTRO(1)
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NAME

6       intro - introduction to user commands
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DESCRIPTION

9       Section 1 of the manual describes user commands and tools, for example,
10       file manipulation tools, shells,  compilers,  web  browsers,  file  and
11       image viewers and editors, and so on.
12
13       All  commands  yield  a status value on termination.  This value can be
14       tested (e.g., in most shells the variable $?  contains  the  status  of
15       the  last  executed  command) to see whether the command completed suc‐
16       cessfully.  A zero exit status is conventionally used to indicate  suc‐
17       cess,  and  a  nonzero  status means that the command was unsuccessful.
18       (Details of the exit status can be found in wait(2).)  A  nonzero  exit
19       status  can  be  in the range 1 to 255, and some commands use different
20       nonzero status values to indicate the reason why the command failed.
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NOTES

23       Linux is a flavor of UNIX, and as a first approximation all  user  com‐
24       mands  under  UNIX work precisely the same under Linux (and FreeBSD and
25       lots of other UNIX-like systems).
26
27       Under Linux there are GUIs (graphical user interfaces), where  you  can
28       point  and  click  and  drag, and hopefully get work done without first
29       reading lots of documentation.  The traditional UNIX environment  is  a
30       CLI  (command line interface), where you type commands to tell the com‐
31       puter what to do.  That is faster and more powerful, but requires find‐
32       ing out what the commands are.  Below a bare minimum, to get started.
33
34   Login
35       In  order  to start working, you probably first have to login, that is,
36       give your username and password.  See also login(1).  The program login
37       now starts a shell (command interpreter) for you.  In case of a graphi‐
38       cal login, you get a screen with menus or icons and a mouse click  will
39       start a shell in a window.  See also xterm(1).
40
41   The shell
42       One  types  commands  to the shell, the command interpreter.  It is not
43       built-in, but is just a program and you can change your shell.   Every‐
44       body  has  her  own  favorite one.  The standard one is called sh.  See
45       also ash(1), bash(1), csh(1), zsh(1), chsh(1).
46
47       A session might go like
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49              knuth login: aeb
50              Password: ********
51              % date
52              Tue Aug  6 23:50:44 CEST 2002
53              % cal
54                   August 2002
55              Su Mo Tu We Th Fr Sa
56                           1  2  3
57               4  5  6  7  8  9 10
58              11 12 13 14 15 16 17
59              18 19 20 21 22 23 24
60              25 26 27 28 29 30 31
61
62              % ls
63              bin  tel
64              % ls -l
65              total 2
66              drwxrwxr-x   2 aeb       1024 Aug  6 23:51 bin
67              -rw-rw-r--   1 aeb         37 Aug  6 23:52 tel
68              % cat tel
69              maja    0501-1136285
70              peter   0136-7399214
71              % cp tel tel2
72              % ls -l
73              total 3
74              drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
75              -rw-r--r--   1 aeb         37 Aug  6 23:52 tel
76              -rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
77              % mv tel tel1
78              % ls -l
79              total 3
80              drwxr-xr-x   2 aeb       1024 Aug  6 23:51 bin
81              -rw-r--r--   1 aeb         37 Aug  6 23:52 tel1
82              -rw-r--r--   1 aeb         37 Aug  6 23:53 tel2
83              % diff tel1 tel2
84              % rm tel1
85              % grep maja tel2
86              maja    0501-1136285
87              %
88       and here typing Control-D ended the session.  The % here was  the  com‐
89       mand  prompt—it  is  the shell's way of indicating that it is ready for
90       the next command.  The prompt can be customized in lots  of  ways,  and
91       one might include stuff like username, machine name, current directory,
92       time, and so on.  An assignment PS1="What next, master? " would  change
93       the prompt as indicated.
94
95       We see that there are commands date (that gives date and time), and cal
96       (that gives a calendar).
97
98       The command ls lists the contents of the current directory—it tells you
99       what  files  you  have.  With a -l option it gives a long listing, that
100       includes the owner and size and date of the file, and  the  permissions
101       people  have  for  reading  and/or changing the file.  For example, the
102       file "tel" here is 37 bytes long, owned by aeb and the owner  can  read
103       and  write  it,  others can only read it.  Owner and permissions can be
104       changed by the commands chown and chmod.
105
106       The command cat will show the contents of a file.  (The  name  is  from
107       "concatenate and print": all files given as parameters are concatenated
108       and sent to "standard output", here the terminal screen.)
109
110       The command cp (from "copy") will copy a file.  On the other hand,  the
111       command mv (from "move") only renames it.
112
113       The  command  diff lists the differences between two files.  Here there
114       was no output because there were no differences.
115
116       The command rm (from "remove") deletes the file, and be careful! it  is
117       gone.  No wastepaper basket or anything.  Deleted means lost.
118
119       The  command  grep (from "g/re/p") finds occurrences of a string in one
120       or more files.  Here it finds Maja's telephone number.
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122   Pathnames and the current directory
123       Files live in a large tree, the file hierarchy.  Each  has  a  pathname
124       describing  the  path  from the root of the tree (which is called /) to
125       the file.  For example, such a full pathname  might  be  /home/aeb/tel.
126       Always  using  full  pathnames would be inconvenient, and the name of a
127       file in the current directory may be abbreviated  by  giving  only  the
128       last  component.   That  is  why  "/home/aeb/tel" can be abbreviated to
129       "tel" when the current directory is "/home/aeb".
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131       The command pwd prints the current directory.
132
133       The command cd changes the current directory.  Try "cd /" and "pwd" and
134       "cd" and "pwd".
135
136   Directories
137       The command mkdir makes a new directory.
138
139       The  command  rmdir  removes  a directory if it is empty, and complains
140       otherwise.
141
142       The command find (with a rather baroque syntax) will  find  files  with
143       given  name or other properties.  For example, "find . -name tel" would
144       find the file "tel" starting in the present directory (which is  called
145       ".").   And  "find  / -name tel" would do the same, but starting at the
146       root of the tree.  Large searches on a multi-GB disk will be  time-con‐
147       suming, and it may be better to use locate(1).
148
149   Disks and filesystems
150       The  command  mount  will attach the file system found on some disk (or
151       floppy, or CDROM or so) to the big file system hierarchy.   And  umount
152       detaches  it again.  The command df will tell you how much of your disk
153       is still free.
154
155   Processes
156       On a UNIX system many user and  system  processes  run  simultaneously.
157       The  one  you  are talking to runs in the foreground, the others in the
158       background.  The command ps will show you which  processes  are  active
159       and  what numbers these processes have.  The command kill allows you to
160       get rid of them.  Without option this is a friendly request: please  go
161       away.   And "kill -9" followed by the number of the process is an imme‐
162       diate kill.  Foreground processes can often be killed  by  typing  Con‐
163       trol-C.
164
165   Getting information
166       There are thousands of commands, each with many options.  Traditionally
167       commands are documented on man pages, (like this one), so that the com‐
168       mand  "man  kill" will document the use of the command "kill" (and "man
169       man" document the command "man").   The  program  man  sends  the  text
170       through  some  pager,  usually less.  Hit the space bar to get the next
171       page, hit q to quit.
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173       In documentation it is customary to refer to man pages  by  giving  the
174       name  and section number, as in man(1).  Man pages are terse, and allow
175       you to find quickly some forgotten detail.  For newcomers an  introduc‐
176       tory text with more examples and explanations is useful.
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178       A  lot  of  GNU/FSF  software  is provided with info files.  Type "info
179       info" for an introduction on the use of the program "info".
180
181       Special   topics   are   often   treated   in    HOWTOs.     Look    in
182       /usr/share/doc/howto/en and use a browser if you find HTML files there.
183

SEE ALSO

185       standards(7)
186

COLOPHON

188       This  page  is  part of release 3.53 of the Linux man-pages project.  A
189       description of the project, and information about reporting  bugs,  can
190       be found at http://www.kernel.org/doc/man-pages/.
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194Linux                             2007-11-15                          INTRO(1)
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