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 user name, 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 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 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.
Copyright (c) 2002 Andries Brouwer <aebcwi.nl> Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. 2007-10-23 mtk Added intro paragraph about section, plus a paragraph about exit status values. |