ch12.htm

linux-unix130.linux.and.unix.ebooks130 linux and unix ebookslinuxLearning Linux - Collection of 12 E

	<LI><TT>kill-whole-line</TT> (<TT>^U</TT>): Deletes all of the characters on the

	current line.

</UL>



<P>All of these commands are the same whether you're in <TT>emacs</TT> or <TT>vi</TT>

insert mode. <TT>tcsh</TT> supports many more editing commands than are listed here.

To see what these commands are, refer to the <TT>tcsh</TT> man page.</P>

<P>The following are examples of setting key bindings:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">bindkey ^W kill-whole-line



bindkey ^S beginning-of-line

</FONT></PRE>

<CENTER>

<H3><A NAME="Heading17<FONT COLOR="#000077">Other Neat Stuff</FONT></H3>

</CENTER>

<P><TT>tcsh</TT> supports a few neat features that none of the other shells discussed

in this book support. This section lists a few of the most useful of these extended

features.

<CENTER>

<H4><A NAME="Heading18<FONT COLOR="#000077">Correcting Spelling Errors</FONT></H4>

</CENTER>

<P>This feature, which is not available with any of the other shells discussed in

this book, is a dream come true for many people (including me). If you're plagued

by recurring typos, this feature might be enough to cause you to use <TT>tcsh</TT>

over any of the other shells. You can tell <TT>tcsh</TT> to correct spelling errors

in a command that you typed, and you also can tell it to automatically try to correct

commands that it can't figure out.</P>

<P>The first function isn't quite as useful, because you must know that you have

made a typing mistake before you actually execute the command. This feature is invoked

by pressing Esc-S on the command line before you press Enter.</P>

<P>For example, suppose you wanted to change to the <TT>/usr/X386/X11/bin</TT> directory,

so you typed the following command on the command line:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">cd /usr/X387/X11/bun

</FONT></PRE>

<P>If you caught the typing errors before you executed the command (by pressing the

Enter key), you could correct the errors by pressing Esc-S. <TT>tcsh</TT> will try

to correct the spelling of the command. It would change the command to read<FONT

COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">cd /usr/X386/X11/bin

</FONT></PRE>

<P>You could now press the Enter key, and the command would execute just as you wanted.

Obviously, this command has some limitations, because the shell can't (yet) read

your mind, but for simple character transpositions or capitalization errors, it works

very nicely.</P>

<P>The second method of instructing <TT>tcsh</TT> to perform spelling corrections

on your commands is to set the correct <TT>tcsh</TT> variable. This variable, depending

on what options you use, will tell <TT>tcsh</TT> to try to correct spelling errors

in command names or anywhere in the command. The syntax for setting the correct variable

is one of the following:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">set correct=cmd  or



set correct=all

</FONT></PRE>

<P>After you set the correct variable, whenever you enter a command that <TT>tcsh</TT>

doesn't understand, it will automatically check to see if the command has any spelling

errors. If it finds possible spelling errors, it gives you the corrected command

and asks you if the new command is what you intended. For example, if you had set

the correct variable with the <TT>all</TT> option and then entered the following

command:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">cd /usr/gmes

</FONT></PRE>

<P><TT>tcsh</TT> would respond with the following prompt on the command line:<FONT

COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">CORRECT&gt;cd /usr/games (y|n|e)?

</FONT></PRE>

<P>If you respond to the prompt by pressing the y (yes) key, <TT>tcsh</TT> will execute

the corrected command. If you respond to the prompt by pressing the n (no) key, <TT>tcsh</TT>

will execute the command that you initially entered, which in turn will cause an

error message to be displayed.</P>

<P>If you respond to the prompt by pressing the e (edit) key, <TT>tcsh</TT> will

put the command that you entered back on the command line and enable you to edit

it.

<CENTER>

<H4><A NAME="Heading19<FONT COLOR="#000077">Precommands</FONT></H4>

</CENTER>

<P><TT>tcsh</TT> supports a way of executing a command prior to displaying each command

prompt. This is done through the use of a special variable called <TT>precmd</TT>.

If the <TT>precmd</TT> variable is set, the command that it is set to will be executed

before the command prompt is displayed on-screen. For example, assume that you set

the <TT>precmd</TT> variable using the following command:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">alias precmd time

</FONT></PRE>

<P>After this alias has been declared, the <TT>time</TT> command will always be executed

before the command prompt is displayed on-screen.

<CENTER>

<H4><A NAME="Heading20<FONT COLOR="#000077">Change Directory Commands</FONT></H4>

</CENTER>

<P><TT>tcsh</TT> also supports change directory commands. These commands are executed

only when the current directory changes (usually as a result of executing the <TT>cd</TT>

command). This type of command is probably more useful than the precommands just

mentioned, because there are times when you might want to know something about a

directory that you just entered.</P>

<P>This feature is supported in the same way precommands are supported, only you

must provide an alias for a different variable. The variable used for this is <TT>cwdcmd</TT>.

If this variable is aliased to a command, that command will be executed each time

you change current working directories.</P>

<P>A common use for this variable is to display the current directory to the screen.

This can be done by entering the command<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">alias cwdcmd `pwd'

</FONT></PRE>

<P>This will display the name of the new directory each time a new directory is entered.



<DL>

	<DT></DT>

</DL>





<DL>

	<DD>

<HR>

<A NAME="Heading21<FONT COLOR="#000077"><B>WARNING:</B> </FONT>You should not

	put a <TT>cd</TT> command into <TT>cwdcmd</TT>. Doing so could cause an infinite

	loop that would cause you to lose control of <TT>tcsh</TT>.

<HR>



</DL>



<CENTER>

<H4><A NAME="Heading22<FONT COLOR="#000077">Monitoring Logins and Logouts</FONT></H4>

</CENTER>

<P><TT>tcsh</TT> provides a mechanism that enables you to watch for any user who

logs on or off the system. It does this through a <TT>tcsh</TT> variable named <TT>watch</TT>.</P>

<P>The <TT>watch</TT> variable contains a set of user ID and terminal number pairs.

These pairs can contain wildcards and also can contain the word &quot;any,&quot;

which tells <TT>tcsh</TT> to match any user or terminal. The syntax for setting the

<TT>watch</TT> variable is<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">set watch=(&lt;user&gt; &lt;terminal&gt;)

</FONT></PRE>

<P>The user in this command refers to a Linux user ID. terminal refers to a Linux

terminal device number.</P>

<P>Most people would use this capability to watch for friends logging onto the system.

For example, if you were waiting for a person with the username <TT>jules</TT> to

come to work in the morning, you could set the following <TT>watch</TT> variable:<FONT

COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">set watch=(jules any)

</FONT></PRE>

<P>This command would inform you when a person with the user ID <TT>jules</TT> logged

into the system on any terminal. <TT>tcsh</TT> defaults to checking the defined watches

every 10 minutes. If you want to know with greater or lesser frequency, you can change

this default by passing the number of minutes to wait between checks as the first

parameter to the <TT>watch</TT> variable. For example, to check every five minutes

to see if <TT>jules</TT> has logged in, you would use the following <TT>watch</TT>

variable:<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">set watch=(5 jules any)

</FONT></PRE>

<P>This will do the same thing as the first command, except it will check every 5

minutes instead of every 10 to see if <TT>jules</TT> has logged in.

<CENTER>

<H3><A NAME="Heading23<FONT COLOR="#000077">Customizing tcsh</FONT></H3>

</CENTER>

<P>I've discussed many ways of customizing <TT>tcsh</TT> in this chapter. If you

just enter the commands that we have discussed at the command line, the changes you

make will be lost every time you log out of the system. This section describes how

to store these changes in a file that will be executed each time you start <TT>tcsh</TT>.</P>

<P>Two initialization files are important to <TT>tcsh</TT>. The first is called the

login file. The commands in this file are executed when you first log into Linux.

The contents of the default login file are shown in Listing 12.2. Listing 12.2. Default

csh.login file.<FONT COLOR="#0066FF"></FONT>

<PRE><FONT COLOR="#0066FF">if ($?prompt) then

umask 022

  set cdpath = ( /usr/spool )

  set notify

  set history = 100

    setenv OPENWINHOME /usr/openwin

    setenv MANPATH /usr/local/man:/usr/man/preformat:/usr/man:/usr/X11/man:

    &#194;/usr/openwin/man

    setenv MINICOM &quot;-c on&quot;

    setenv HOSTNAME &quot;'cat /etc/HOSTNAME'&quot;

    set path = ( $path /usr/X11/bin /usr/andrew/bin 

         &#194;$OPENWINHOME/bin /usr/games . )

endif

# I had problems with the Backspace key installed by `tset,' but you might want

# to try it anyway, instead of the `setenv term.....' below it.

# eval `tset -sQ &quot;$term&quot;`

# setenv term  linux

#if ! $?TERM setenv TERM linux

# set to &quot;linux&quot; for unknown term type:

if (&quot;$TERM&quot; == &quot;&quot;) setenv TERM linux

if (&quot;$TERM&quot; == &quot;unknown&quot; setenv TERM linux

set prompt = &quot;%m:%~%# &quot;

eval 'dircolors -t' # set up color-ls variables

alias ls `ls -F'

if ( { tty --silent } ) then &gt;&amp; /dev/null

  echo &quot;&quot;;fortune;echo &quot;&quot;

endif

</FONT></PRE>

<P>This file, <TT>csh.login</TT>, can be found in the <TT>/etc</TT> directory. If

you want to change any of the settings found in <TT>csh.login</TT>, you should copy

it to your home directory, rename it <TT>.login,</TT> and make the changes you want

there.</P>

<P>The other file that <TT>tcsh</TT> makes use of is <TT>cshrc</TT>. The commands

in this file are executed each time a copy of the <TT>tcsh</TT> program is run. Examples

of the types of commands that usually appear in this file are aliases and variable

declarations. This file, <TT>csh.cshrc</TT>, is also contained in the <TT>/etc</TT>

directory. If you want to make changes to this file, you should copy it to your home

directory, rename it <TT>cshrc</TT>, and make your changes there.</P>

<P>When you first log in to Linux, <TT>tcsh</TT> executes the <TT>/etc/csh.cshrc</TT>

file, followed by the <TT>/etc/csh.login</TT> file. It then checks your home directory

to see if you have a personal copy of the <TT>csh.cshrc</TT> file. This file can

be named either <TT>.tcshrc</TT> or <TT>.cshrc</TT>. If you have one of these files

in your home directory, <TT>tcsh</TT> will execute it next.</P>

<P><TT>tcsh</TT> next checks to see if you have your own copy of the <TT>csh.login</TT>

file in your home directory. This file must be named <TT>.login</TT>. If you do have

a <TT>.login</TT> file in your home directory, it will be executed next.</P>

<P>Whenever you start another copy of <TT>tcsh</TT> after you log in to the system,

it will execute the commands that are in the <TT>/etc/csh.cshrc</TT> file and then

check your home directory to see if there is a <TT>.tcshrc</TT> or a <TT>.cshrc</TT>

file there.

<CENTER>

<H3><A NAME="Heading24<FONT COLOR="#000077">tcsh Command Summary</FONT></H3>

</CENTER>

<P>Here are some of the most useful <TT>tcsh</TT> commands:



<UL>

	<LI><TT>alias</TT>: Used to set and display aliases, command nicknames that can be

	set by the user.

	<P>

	<LI>bg: Background command. Forces a suspended process to continue running in the

	background.

	<P>

	<LI><TT>bindkey</TT>: Enables users to change the editing actions that are associated

	with a key sequence.

	<P>

	<LI><TT>cd</TT>: Changes the current working directory to the directory specified.

	<P>

	<LI><TT>exit</TT>: Terminates the shell.

	<P>

	<LI><TT>fg</TT>: Foreground command. Forces a suspended process to continue running

	in the foreground.

	<P>

	<LI><TT>history</TT>: Enables users to display and modify the contents of the history

	list and the history file.

	<P>

	<LI><TT>kill</TT>: Terminates another process.

	<P>

	<LI><TT>logout</TT>: Terminates a login shell.

	<P>

	<LI><TT>set</TT>: Used to set the value of <TT>tcsh</TT> variables.

	<P>

	<LI><TT>source</TT>: Reads and executes the contents of a file. This command is discussed

	in more detail in Chapter 13.

	<P>

	<LI><TT>unalias</TT>: Used to remove aliases that have been defined using the <TT>alias</TT>

	command.

</UL>



<CENTER>

<H3><A NAME="Heading25<FONT COLOR="#000077">tcsh Variables</FONT></H3>

</CENTER>

<P>Here are some of the most useful <TT>tcsh</TT> variables:



<UL>

	<LI><TT>autocorrect</TT>: If this is set, <TT>tcsh</TT> will automatically try to

	correct command-line spelling errors.

	<P>

	<LI><TT>histfile</TT>: The name of the file that is used to store the command history.

	<P>

	<LI><TT>history</TT>: The size of the history list.

	<P>

	<LI><TT>home</TT>: The user's home directory.

	<P>

	<LI><TT>path</TT>: The search path that <TT>tcsh</TT> uses when looking for executable

	programs.

	<P>

	<LI><TT>prompt</TT>: The first-level prompt that is displayed on the command line.

	<P>

	<LI><TT>prompt2</TT>: The second-level prompt that is displayed when a <TT>for</TT>,

	<TT>foreach</TT>, or <TT>while</TT> loop is expecting input.

	<P>

	<LI><TT>prompt3</TT>: The third-level prompt that is displayed when <TT>tcsh</TT>

	has attempted to correct a spelling error in a command.

	<P>

	<LI><TT>savehist</TT>: This variable must be set to the number of history commands

	that you want to save, if you want <TT>tcsh</TT> to save the history list when you

	log out.

	<P>

	<LI><TT>watch</TT>: Contains a list of user terminal pairs to watch for logins and

	logouts.

</UL>



<CENTER>

<H3><A NAME="Heading26<FONT COLOR="#000077">Summary</FONT></H3>

</CENTER>

<P>The last three chapters have presented the fundamental commands and concepts of

the three most popular UNIX shells. <TT>tcsh</TT> is the most feature-rich shell

of those presented, but that doesn't necessarily mean that it's the best shell for

you to use. In the end, this decision will probably be based on your personal preference

as opposed to what features are offered.</P>



<P>The next chapter looks at the programming languages that are provided by each

of the shells we have discussed.









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