function f-tutorial.4 ()
{
clear
bold
cyan
echo "In Which we Search for Magritte's Pipe"
echo
white
cat << EOI

So far we have made a few files, ordered a cat around, clobbered some information, and discovered 
one of many editors.

Now, any GNU/Linux system has a mind-boggling number of files, containing an extraordinary 
amount of information. This is both good and bad.

Finding what you are looking for can be a challenge. Several tools have been devised to make this
easier. Some search directly in real time, and others use a database, updated at regular intervals.

We'll start with the most sensibly named command, which uses the database approach. The command is

EOI
yellow
echo "locate"
echo
white

cat << EOL
Now "locate" is less immediately useful on a live CD, because it does nothing without having
a database to work with. On an installed system, updatedb is usually run automatically at some
early morning hour, daily. Thus the database is always slightly "out of date".

If you try, for example, "locate .ogg" for the first time on this CD, locate will complain.

You will see:  locate: /var/cache/locate/locatedb: No such file or directory

which is locate's way of telling you that it has absolutely no idea how to find anything...

EOL
echo "If you haven't already run \"sudo updatedb\" try typing:"
yellow
echo
echo "locate .ogg  (then exit or CTRL+D, of course)"
white
echo
unbold
/bin/bash
bold
echo
echo "We can fix that by running:"
yellow
echo
echo "sudo updatedb"
echo
cyan
echo "As usual in these tutorials, hit <space> to continue, m for the menu, x for a prompt..."

f-tutescape
echo
cyan
echo "Give me back my command prompt!"
echo

white

cat << EOB
This brings up at least three interesting points worth knowing about.

First:

* combing the whole filesystem from "/" down to build a database can take quite a while.
If we issue the command "sudo updatedb", we will be watching a blinking prompt until it finishes.

Second:  

* updatedb needs to be run with "administrative" privileges, because it needs to access all
files, and your user does not have permission to do this. That is why we put "sudo" in front of 
the command.

Third: 

* having a "long" job running in the "foreground" like this is usually impractical, or just 
plain annoying. It takes over our current terminal - until it finishes, and gives us back
our command prompt.

Rather than pursue the use of "locate" now, let's see how the Unix gurus got around this issue.

EOB
f-tutescape

echo
cyan
echo "Get out of my way!"
white
echo
cat << EOJ
They came up with a clever dodge called "job control". By using a few tricks, we can shove our
long job out of the way, while we continue to issue other commands at the prompt.

We won't go into a lot of detail about this - just give a few useful methods.

The first and most common form of job control is to start a "takes a while" command
with "&" appended, to "background" it immediately.

So you would think, in the case of "updatedb" that we would type:

EOJ
yellow
echo "sudo updatedb &"
white
echo

cat << EOX
Actually, because "sudo" is a special command that gives us administrative powers, this is not
the right way for this case. It will work on this live CD, because sudo does not prompt for a 
password. On a more usual system, the problem with this command is that it immediately goes to 
the background, without being able to give us a password prompt. This confuses matters. 

To avoid this we instead type:

EOX
yellow
echo "sudo -b updatedb"
white
echo
echo "So as a practical exercise, type that last command in the shell below, then exit to return"
echo "to the tutorial. If you do it right, you will get your prompt back, and can let updatedb"
echo "do its job while continuing with this tutorial."
echo
echo "Throughout this tutorial, remember to \"exit\" or \"CTRL+D\" after each exercise, as usual."

unbold
echo
/bin/bash
bold
echo

cat << EOC
This is rather a special case, of course.

More often, we find ourselves in the situation where we have started a command that is taking
longer than expected. The cursor is blinking at us malevolently, as if to say "You can't have
your command prompt back!".

We can fix that...
EOC
f-tutescape
echo
cyan
echo "The trick here is to type:"
echo
yellow
echo "CTRL+Z"
echo
white
echo "... which stops the process in its tracks, without killing it." 
echo "    That is not much use until we follow with:"
echo
yellow
echo "bg"
white
echo
echo "... which puts the process in the "background" to continue, and gives us our prompt back."
echo
echo "We can bring the job back to the foreground by typing:"
echo
yellow
echo "fg"
white
echo
echo "While the job is running in the foreground, we can either kill it with:"
yellow
echo
echo "CTRL+C"
white
echo
printf "Or repeat the sequence by putting it back in the \"background\" with"
yellow
printf " CTRL+Z" ; white ; printf ", followed by" ; yellow ; printf " bg" 
echo
white
echo "We'll try this with the ubuntu_sax.ogg file that happens to be in /usr/share/example-content."
echo
echo "You can access this directly, or via a link in your $HOME directory." 
echo
echo "The one in $HOME is linked to /usr/share/example-content -"
echo "so using "example-content/ubuntu_sax.ogg" from $HOME is the same as using the path above."
echo
echo "Cheat sheet on the next page..."

f-tutescape

echo
cyan
bold
echo "Cheat sheet for job control experiments"
white
echo
echo "At the subshell prompt below, type these commands in order, with a few seconds in between:"
echo "Remember tab completion!"
yellow
echo
echo "ogg123 -q /usr/share/example-content/ubuntu_sax.ogg"
echo
echo "CTRL+Z"
echo
echo "bg"
echo
echo "fg"
echo
echo "CTRL+C"
echo
cyan
echo "Don't leave out the -q (for \"quiet\"),"
echo "or ogg123 will continue to print information to your screen while in the background :)" 
echo
white
echo "That gets confusing..."
echo
unbold
/bin/bash
bold
echo
echo "OK - you will have seen some output like [1]... and the command shown, and probably also a"
echo "message from ALSA - the Advanced Linux Sound Architecture. These messages are harmless :)"
echo
echo "I suggest trying the exercise again, this time alternating CTRL+Z with the"
yellow ; printf "bg" ; white ; printf " and" ; yellow ; printf " fg" ; white ; printf " commands."
echo
echo "Don't forget that you can stop the playing with CTRL+C while it is in the foreground."
cyan
echo
echo "Here's another prompt:"
echo
white
unbold
/bin/bash
bold
echo
echo "You might be wondering at this point where \"locate\" went, and why we are digressing..."

f-tutescape

echo
cyan
echo "What can locate do now?"
echo
white
echo "If you ran updatedb as suggested earlier, it should have overcome its amnesia by now ;-)"
echo "If it still can't find its database, give it a while longer to finish updating, and try again."
echo
echo "Let's see what "
echo
yellow
echo "locate .ogg"
white
echo
echo "gives us this time..."
echo
unbold
/bin/bash
bold
echo
echo "That should be a bit more useful than before..."
echo
echo "On most systems, \"locate .ogg\" would return a lot of output - much"
echo "more than one screen."
echo
echo "So how do we handle such output?"
echo
echo "You will remember that we used the \"less\" pager to read long files..."
echo
echo "This is a different case though - we are dealing with actual output from a command."
echo
echo "Well, that can be fixed too..."

f-tutescape

echo
cyan
echo "Connecting Programs."
printf "\n\n"
white
echo "You recall that the Unix philosophy is to use programs that do one thing well, and"
echo "connect them together to make more complex tasks possible. One of the methods is"
echo "symbolised by:"
yellow
echo
echo "			|"
echo
white
echo "This is known as a pipe. We can feed output from one program through this \"pipe\""
echo "to another program that handles the output for us."
echo
echo "Try typing:"
echo
yellow
echo "locate apt | less"
echo
white
echo "at the prompt below. Remember that the \"less\" pager can be navigated with the space bar"
echo "or arrow keys, and that you can use \"/searchterm\" to look for things in it. q for quit..."
echo
echo "Reminder: When you exit \"less\" you are at a prompt. Type exit or CTRL+D to return to the"
echo "tutorial."
echo
unbold
/bin/bash
bold
echo
echo "As you see, the output of the locate command is fed to \"less\", which makes it readable."
echo "Another tool makes an appearance on our next page ( well, our next screen I suppose...)"

f-tutescape
echo
cyan
echo "Grab Really Exceptional Patterns"
echo
white
echo "The above line will make geeks' blood boil... The acronym we are introducing here is"
echo
yellow
echo "grep"
white
cat << EOG

No-one seems to be quite sure what it actually stands for, but you will see
"Global Regular Expression Parser" , "Global Regular Expression Print" , and of course
the most likely one, "GREen Parakeet".

grep is really useful, whatever you decide it stands for - and you really don't need
to know what a "Regular Expression" is to use it.

In the simplest case, we can use grep to find words in a file. The output will show the
line in which each instance of the word appears.

In the shell below, check that you are in $HOME then type:

EOG
yellow
echo "grep INX about-inx"
echo
white
unbold
/bin/bash
bold
echo
cat << EOE
Grep returns each line on which the "pattern" INX occurs in the file "about-inx"

Big deal, you say...

Well, let's do some more Unixish "grepping"...

Suppose we want to find out information about the "apt" software installation
and removal tool. We can combine the locate command with grep and less like
this, for example:
EOE
echo
yellow
echo "locate apt | grep -v aptitude | less"
echo
white
echo "What does the -v do? It is one of the useful options for grep, and means"
echo "\"Don't include this pattern in the search\" - so we are eliminating \"aptitude\""
echo "in this case."
echo
echo "Try it below:"
echo 
unbold
/bin/bash
bold
echo
echo "Of course, as you see, we still get some irrelevant results, but they are easy to spot."
echo
echo "Another useful option is -i , which makes our search \"case insensitive\". "
echo
echo "You are probably aware by now that GNU/Linux is picky about case :) A file named INX"
echo "is not the same as a file named inx, or inX, and so on."
echo
echo "grep can also rather cleverly search through a directory \"recursively\" that is, "
echo "including its sub-directories. For example:"
echo

yellow
echo "grep -ir INX /usr/local/* | less"
white
echo
echo "Try that to see - notice that grep tells you which files contain the strings it finds."
echo "The \"-r\" in grep -ir of course means \"recursive\" . As it happens, all the INX and inx"
echo "references happen to be in /usr/local/bin :)"
echo
unbold
/bin/bash
bold
echo
white
echo "You might have noticed that last command introduced an extra character at the end of"
echo "the file path."
echo
echo "This is known as a \"wild card\" or \"metacharacter\"."
echo
echo "If you are curious about this, try a google search on the terms"
echo
echo "linux bash globbing"
echo
echo "To keep things slightly less mind-boggling, we will just note two useful wildcards"
echo "here:"
echo
echo " *   means \"match any number of characters\""
echo " ?   means \"match just one character\""
echo 
echo "For example, suppose you are looking for file names in the current directory ending with" 
echo "the string \"dm\" and only one leading character before the \"dm\""
echo
echo "You can type"
echo 
yellow
echo "ls ?dm "
white
echo
echo "More generally useful is the * wildcard - for instance you can match all .ogg files in"
echo "a directory with:"
echo
yellow
echo "ls *.ogg"
white
echo
echo "So, as an example, to play all the Ogg Vorbis tracks in a directory you could type:"
echo
yellow
echo "ogg123 -q *.ogg"
white
echo
echo "... then use CTRL+Z, bg ,fg and CTRL+C to put them in the background, start and stop them,"
echo "and so on. A quick and dirty music list player. There are better ways in this instance, of course."

f-tutescape
echo
cyan
echo "Special Characters."
white
cat << EOS0

Bash has certain characters that can cause issues, because they have a special meaning.
This is both useful and occasionally frustrating.

The most obvious case is the "space" character. As far as bash is concerned, a space
means either that the next string is a command, ( that could include seemingly unlikely things 
like "[" ), or an option, if preceded by " - ", or another file name, and so on.

This actually  makes sense, but drives former users of other operating systems nuts, 
because they are usually in the habit of using multi-word file names with spaces. 

Tip: in Unix and GNU/Linux, make a habit of naming files that have multiple words as 

this-file , or this_next_file or this.other.file

Tip: you can tab-complete file names with spaces. 

So, for example, to play your innocent new video named 
"Blood Violence and Gratuitous Sex.avi", with mplayer, try

EOS0
yellow
echo "mplayer Bloo <tab>"
white
echo
echo "You will notice that what bash shows is Blood\\ Violence\\ and\\ Gratuitous\\ Sex.avi"
echo
echo "Bash has \"escaped\" the spaces with backslashes for you."
echo "You can do this laboriously yourself, of course, but it would be a bit pointless"
echo "if tab completion does it for you."
echo
echo "Another way to make spaced file names understood in bash is to quote them."

f-tutescape
echo
echo
echo "Other characters that are \"special\" to Bash include:"
yellow
cat << EOSP

	!
	#
	;
	.
	\\
EOSP
white
cat << EOSP1

Because their meaning is dependent on context, there is too much here to cover in this
tutorial. A google search on

linux bash special characters	

will turn up some further explanation - for example

http://tldp.org/LDP/abs/html/special-chars.html

EOSP1

f-tutescape
echo
cat << EOCH

Some are very useful on the command line. For example we can use the bash "history" with "!" .

! is one of those context-dependent special characters. It can also mean "not" and is often
so used in bash script constructs. Using it with the Bash history is more useful from the 
command line...
EOCH
yellow
cat << EOOGG

!ogg

EOOGG
white

echo "will execute the last command we used starting \"ogg\" ( ogg123 for instance)."
yellow
cat << EODOLL

!$

EODOLL
white
cat <<EOAPP
will append the last "argument" we used (on the previous line) to the command we are typing. 
So if we want to replay the same .ogg file we just played, but without the -q option to ogg123, 
we can type

EOAPP

yellow
echo "ogg123 "\!""\$""
white
echo
echo "The dot character can mean a \"hidden\" file like, say, .screenrc . It can also mean"
echo "\"this\" or \"this right here\" or \"this directory\". So we often do something like:"
echo
yellow
echo "cp /some/path/to/file-we-want-a-copy-of . "
white
echo
echo "Which will copy the file to our current working directory."
echo

 
f-tutescape
echo ; cyan
echo "Remember Magritte?"
white
echo
echo "Well, we have been dealing with symbols... so see what you make of this:"
cat << EOMAGRITTE

" . ! 1 | "  --  Magritte's Computer"

That was seen as a "signature" on a mailing list. See if you can decode it :)

EOMAGRITTE
cyan
echo "That's it for tutorial 4. The usual key escapes apply..."
f-tutescape
f-tutorial
}