6.3.1 System-Wide Versus User-Specific Configuration
It’s important to remember that there are two different kinds of configurations on a Debian system. _System-wide configuration_ affects all users. System-wide settings are made in the /etc directory, so you generally must be root in order to change system-wide settings. You might configure the way the system connects to the Internet, for example, or have web browsers on the system always start on the company home page. Since you want these settings to apply to all users, you make the changes in /etc. Sample configuration files in /etc include /etc/X11/XF86Config, /etc/lynx.cfg, and /etc/ppp/options. In fact, nearly all the files /in /etc are configuration files.
_User configuration_ affects only a single user. Dotfiles are used for user configuration. For example, the file ~/.newsrc stores a list of which USENET (discussion group) articles you have read and which groups you subscribe to. This allows news readers such as trn or GNUS to display unread articles in the groups you’re interested in. This information will be different for every user on the system, so each user has his own .newsrc file in his home directory.
If you use the same command often, you might get tired of typing it. bash lets you write shorter _aliases_ for your commands.
Say you always use the -almost-all and -color=auto options to ls. You quickly get tired of typing ls -almost-all -color=auto. So you make an alias:
Now you can type myls instead of the full command. To see what myls really is, run the command type myls. To see a list of aliases you’ve defined, simply type alias on a line by itself.
[Illustration: Figure 6.3: Redirecting output]
Throughout your experiences with Linux, you will most likely find that manipulating application input and output can be a very powerful thing to do. This section describes some of the things that controlling input and output can do for you.
6.5.1 stdin, stdout, Pipelines, and Redirection
Every process has at least three connections to the outside world. The _standard input_ is one source of the process’s data; the _standard output_ is one place the process sends data; and the _standard error_ is a place the process can send error messages. (These are often abbreviated stdin, stdout, and stderr.)