Chapter 5. Setting Up Your Terminal

In This chapter:

  • Identifying Your Terminal Settings

  • What the Settings Mean

  • Changing Your Terminal Settings

  • Did Your Terminal Stop Working?

You interact with the shell through your keyboard, so it’s important to know which keys have special functions for controlling your terminal:[6]

  • As you issue commands, you’re bound to make typing mistakes. You can correct them by backspacing over characters or words and then retyping, or you can erase the entire line to start over.

  • Sometimes, you’ll want to move a slow-running command into the background so you can continue working, or kill a command that starts spewing out more output than you expected. These operations are done by typing special keys.

This chapter explains how to use the stty command to find out what your key settings are, and how to change them if you don’t like them. Your terminal is a tool that you control — it shouldn’t control you.

Identifying Your Terminal Settings

stty displays your current terminal settings. Its options vary from system to system, but at least one of the following command lines should produce output identifying several important terminal control functions and the characters you type to perform them:

% stty -a
% stty all
% stty everything

In the output, look for something like this:

erase kill werase rprnt flush lnext susp intr quit stop  eof
^?    ^U   ^W     ^R    ^O    ^V    ^Z   ^C   ^   ^S/^Q ^D

Or like this:

intr = ^c; quit = ^; erase = ^?; kill = ^u; eof = ^d; start = ^q;
stop = ^s; susp = ^z; rprnt = ^r; flush = ^o; werase = ^w; lnext = ^v;

The words erase, kill, etc., indicate terminal control functions. The ^c sequences indicate the characters that perform the functions. For example, ^u and ^U represent CTRL-U, and ^? represents the DEL character.

What the Settings Mean

There are many special keys on your terminal; the most important are those that per form the erase, kill, werase, rprnt, lnext, stop, start, intr, susp, and eof functions.

Line Editing Settings

The erase, kill, werase, rprnt, and lnext characters let you do simple editing of the current command line. (Some systems do not support werase or rprnt.) If you use tcsh, you also have access to a built-in general purpose editor, described in Chapter 7, The tcsh Command-Line Editor.

erase

To backspace over the last character, type the erase character. Common erase characters are CTRL-H (also known as BACKSPACE) or DEL. Terminals vary in what they provide. There is often a BACKSPACE key that produces CTRL-H, and/or a DEL (or DELETE or RUBOUT) key that produces a DEL character. Some keyboards have only a BACKSPACE or DEL key, but allow you to program the key to produce the character you want.

kill

The kill (line kill) character completely zaps the line you’re typing so you can start over. Common kill character settings are CTRL-U or CTRL-X.

werase

The werase (word erase) character erases the last word of your command line with one keystroke. When you need to erase several characters, using word erase is often faster than hitting the erase key over and over. The werase key is usually CTRL-W. (If you’re using tcsh, CTRL-W might not do word erase. Try ESC DEL or ESC CTRL-H instead.)

rprnt

The rprnt (reprint) character redisplays the command line you’re typing—useful if output gets splattered into the middle of your command line (e.g., from a background process, or from line noise over a modem connection). By reprinting the command line, you can see what you had typed. The rprnt character is usually CTRL-R.

If you are on a System V UNIX machine, don’t be fooled by documentation that says this control function is named reprint. The stty command actually recognizes rprnt.

lnext

The lnext (literal-next) character lets you type characters into the command line that would otherwise be interpreted immediately. For instance, in tcsh, TAB triggers filename completion. To type a literal TAB into a command, type the lnext character first. The lnext character is usually CTRL-V.

Process Control Settings

The stop, start, intr, susp, and eof characters allow you to control running processes.

stop, start

The stop character stops output to your terminal until you type the start character. These characters help you control the flow of output to your terminal.[7] The stop and start characters are usually CTRL-S and CTRL-Q. Some terminals have a “scroll lock” key that alternately generates CTRL-S and CTRL-Q.

intr

If you issue a command that takes too long to finish, or that runs away by producing too much output, you can usually kill it by interrupting it. The usual intr character is CTRL-C.

If the command that you want to interrupt disables CTRL-C to make itself uninterruptible, try suspending the command with CTRL-Z. Then, kill it like this:

% kill %                          Try this first
% kill -9 %                       Try this if plain kill doesn't work

The kill character is different than the kill command; the former erases your current command line, while the latter clobbers a running program.

susp

If you want to move a command into the background (e.g., if it’s taking a long time to finish), first suspend it by typing the susp character (usually CTRL-Z). Then, resume the command in the background like this:

% bg
eof

The eof character signals end-of-file to the process currently reading the terminal. If this process is the shell, the shell terminates. The eof character is usually CTRL-D. To prevent CTRL-D from terminating your shell, set the ignoreeof variable in your ˜/.cshrc file:

set ignoreeof

Then you’ll need to type exit or logout explicitly.

Changing Your Terminal Settings

If you don’t like your terminal’s settings, use stty to change them:

% stty function char

function is the control function name and char is the associated character. For example, the following command sets the interrupt character to CTRL-C:

% stty intr ^c

You can use either ^c or ^C; stty understands them both to mean CTRL-C.

To make sure your terminal is set up properly each time you log in, put the appropriate stty commands in your ˜/.login file, following any tset or reset commands that might already be in the file. Remember to log in again so that your changes take effect. (For information about your ˜/.login file, see Chapter 4, The Shell Startup Files.)

The next two sections describe how to deal with some common problems involving the erase and line kill characters. If you think your terminal acts funny even after setting it up with stty, look at another user’s ˜/.login file or take a look at the stty manual page. You might find something specific to your system that needs to be set.

Problems Typing the # and @ Characters

On many systems, # and @ are the default erase and kill characters. These choices come from the days of hardcopy terminals and are no longer useful. If your ˜/.login file doesn’t set erase and kill to something else, you may have a hard time typing # and @. Set the kill character in your .login file as shown below; CTRL-U is a common choice:

stty kill ^u

Set the erase character as described in the next section.

Getting Your Terminal To Backspace

Everybody makes mistakes while entering commands, so it’s important to know how to erase typing errors. Usually, you would hit the BACKSPACE or DEL key. If you have trouble backspacing, it’s probably because the system and you don’t agree on what the erase character should be. If you see ^H when you try to erase characters, then your terminal is sending CTRL-H (another name for the BACKSPACE character). Add the following to your ˜/.login file to tell the system to interpret CTRL-H as the erase character:

stty erase ^h                       Set erase character to CTRL-H

If you see ^? when you try to erase, your terminal is sending DEL. Put the following in ˜/.login, to tell the system to interpret DEL as the erase character:

stty erase '^?'                     Set erase character to DEL

Note that ^? should be quoted as '^?' or ^? to turn off the special meaning that the ? character has to the shell as a pattern matching operator.

Did Your Terminal Stop Working?

If your terminal seems to be locked, you may have inadvertently typed CTRL-S, which stops terminal output. To get it going again, type CTRL-Q. Even if CTRL-S wasn’t the problem, CTRL-Q won’t do any harm.

It’s also possible for your terminal to become confused, even if it’s normally set up correctly. This situation can occur for several reasons:

  • You ran a program that set your terminal to a special mode, but crashed before resetting it.

  • You tried to display a binary file or a directory:

    % more core
% more /bin/cat
% more .

  • You logged in over a noisy modem connection. Garbage characters generated on the line can have adverse effects.

If your terminal is left in an unusable state under these or similar circumstances, try the following remedies:

  • First, try CTRL-Q, in case a stray CTRL-S was sent to your terminal.

  • If that doesn’t work, type CTRL-J reset CTRL-J. (If character echoing was turned off, you might not see anything as you type.) The reset command might at least get you to the point at which you can log out and then back in, to re-establish your normal working environment.

  • Finally, try CTRL-C to interrupt your current job, or CTRL-Z to suspend the job so that you can use kill to kill it.


[6] By terminal, I mean a keyboard-display combination. The display could be the screen of a real terminal, an xterm window running under X, or a screen managed by a terminal emulation program, running on a microcomputer.

[7] A better alternative is to pipe command output through more.

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