NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON
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 non-zero status
means that the command was unsuccessful. (Details of the exit status can be
found in wait(2).) A non-zero exit status can be in the range 1 to 255, and
some commands use different non-zero 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).
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.
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 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).
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 Control-C.
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.
standards(7)
This page is part of release 3.21 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2007-11-15 INTRO(1)