man > intro(1)

intro(1)                               General Commands Manual                              intro(1)

NAME
       intro - introduction to user commands

DESCRIPTION
       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.

NOTES
       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.

   Login
       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 their 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  calen‐
       dar).

       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 screen.)

       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 ~".

   Directories
       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.

   Processes
       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  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 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.

SEE ALSO
       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), standards(7)

Linux man-pages 6.7                          2023-10-31                                     intro(1)