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 user commands under UNIX work similarly
under Linux (and lots of other UNIX-like systems too, like FreeBSD).
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 com-
puter what to do. This is faster and more powerful, but requires find-
ing out what the commands are and how to use them. Below is a bare min-
imum guide to get you started.
Login
In order to start working, you'll probably first have to open a session.
The program login(1) will wait for you to type your username and pass-
word, and after that, it will start 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 into the shell, the command interpreter. It is not
built-in; it is just another program. You can change your shell, and
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 look like this:
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, mas-
ter? " 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 in-
cludes the owner and size and date of the file, and the permissions peo-
ple 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 de-
scribing 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 compo-
nent. That is why /home/aeb/tel can be abbreviated to tel when the cur-
rent 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 oth-
erwise.
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 de-
taches 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 back-
ground. 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 com-
mand "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 introduc-
tory 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)
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