function f-tutorial.6 ()
{
bold ; cyan
clear
echo
echo "In Which We Spy and Dig" 
white
cat << EORECAP

We now have some idea how to find information in the system with "locate" and "grep".

We also saw how useful it can be to string commands together with a pipe.

Here we look at what is going on behind the scenes, and learn some simple ways to find
information. We also touch on the beginnings of scripting, without becoming too advanced on
the subject.

EORECAP
cyan
echo "Who is Who"
white

cat << EOWHO

GNU/Linux is designed as a multi-user system. A lot of the time, if you are using the system
as an individual, for example on a home system, this will not be obvious - and might even 
seem irrelevant.

The concept of a "user" is not quite what you might expect, though. Users may or may not be 
actual humans!

You are likely to be the only "user" currently running INX. How does the operating system see
things, though?

At the prompt below, type

EOWHO
yellow
echo "who"
white 
echo
echo "As usual, exit or CTRL+D to return..."
unbold
echo
/bin/bash
echo
bold
cat << EOEXPLAIN

The system thinks there are several of you!
From its viewpoint, this is of course perfectly correct.

The user $USER is logged in on several tty devices.

If, for example, this was a remotely accessible system, or a server for a number of users,
you would see the various user names in the output of "who". This is handy if you feel
nasty and want to kick someone off the system ...

Funnily enough, you can get more useful information with a one letter command. At the
prompt below, type

EOEXPLAIN

yellow
echo "w"
white ; unbold ; echo

/bin/bash
bold
echo
echo "Now you know what those miscreants are up to."
echo "The \"what\" column on the right tells you the latest silly thing each user has"
echo "tried to tell the machine to do!"

f-tutescape

bold ; cyan ; echo
echo "Processes" 
white

cat << EOPROCESS

The machine keeps track of what is happening using process numbers. These are known as
"Process ID" or "PID" for short. Knowing this is often useful. If something is not quite
right, we can often identify the culprit using commands that show us the PID, and more.

The simplest commands of this kind are

EOPROCESS

yellow ; bold
echo "pidof"
echo
echo "pgrep"
white
echo
echo "The second one should look vaguely familiar..."
echo
echo "We can use these to find out the pid for particular running processes."
echo "For example here is the current output of \"pgrep menu\""
echo "(if it's blank then \"menu\" is not running)"
echo
pgrep menu
echo
echo "If we needed to stop that process, we could type \"kill <number here>\""
echo
echo "A quicker way, using a bit of Bash magic, would be"
echo ; yellow 
echo "kill \$(pgrep menu)"
white
echo
echo "Here we are using Bash to substitute the result of the command."
echo "The same result can be achieved by using \"backticks\" instead of the \$( ) syntax:"
yellow ; echo
echo "kill \`pgrep menu\`"
white ; echo
echo "But of course, there's yet another way... as so often in UNIX and GNU/Linux."
yellow ; echo
echo "pkill menu"
white ; echo

f-tutescape
echo
bold ; cyan ; echo
echo "More Spying Methods."
white
cat << EOSPY

While we are on the subject of cloak-and-dagger commands like "kill"...
It's not quite as bad as it sounds - actually the "kill" command is a way to send
"signals" to processes. Not all of these signals actually terminate processes. To know
more have a look at

EOSPY
yellow
echo "man signal"
white

echo
echo "To find manual pages related to a particular command, you can type"
yellow ; echo
echo "apropos <command>"
white ; echo
echo "or"
echo ; yellow
echo "man -k <command>"
white ; echo
echo "I prefer \"apropos\" - it has a ring to it!
Either will identify relevant man pages."
echo
echo "In the shell below, try typing "
yellow ; echo
echo "apropos kill"
white ; echo ; unbold
/bin/bash
bold ; echo
echo "The point here is not that you should immediately read and understand the manual,
but that this is a useful way to find a manual..."
echo
echo "The most important command for spying on what the machine is up to is probably"
echo ; yellow
echo "ps"
white ; echo
echo "Now this little two-letter command looks innocuous enough, but its options are many."
echo
echo "We'll look at a few of them, because \"ps\" is so often useful."

f-tutescape
echo
cyan ; bold ; echo
echo "Forests and Trees."
white ; echo
cat << EOPSBASIC

The command "ps" tells us what processes are running on the current tty ( virtual terminal ).

Digression: Virtual terminals are designated "tty" because originally they were actual "TeleTYpes"

So here is the current output of "ps" on this "tty"...

EOPSBASIC
unbold
ps
bold
cat << EOPSBASIC1

As you can see, not much appears to be happening... but this is an illusion, because there are
potentially five other tty devices also running...

So, we add the option "a" ...

Now we can see rather more - all the other ttys, and users.

EOPSBASIC1
yellow
echo "ps a" ; echo
white ; echo
echo "Hit <space> to see the output."

f-tutescape

unbold
echo
ps a
bold ; echo
echo "Now we add x, so the command becomes"
yellow ; echo
echo "ps ax"
white 
echo
echo "We are going to need to pipe this one through \"less\" - as you will see"
yellow ; echo
echo "ps ax | less"
echo ; white
echo "Hit <space> to see the new output (q to quit from \"less\", of course..."

f-tutescape
unbold
ps ax | less
echo ; bold
echo "Rather a lot of information here..."
echo
echo "So what does the \"x\" do?

It includes all the processes that are running as other \"users\", and those that have
no associated tty. So now we see all the stuff that is propping the system up and
letting us run our programs."
echo
echo "We probably would like to know which user is running which process. So we add \"u\" .
Notice that ps is unlike most commands in that these options do not have a leading \" - \".
The command *can* use such options, but that is something you might want to explore by typing"
echo ; yellow ; bold
echo "ps -help"
white ; bold ; echo

f-tutescape 
bold ; cyan ; echo
echo "Not Seeing the Forest for the Trees."
white ; echo
echo "The output of "ps aux" is too long to be useful, most of the time. Usually we want
to know about a particular program or user. We can apply what we have learnt about grep and
pipes to the problem. So let's say we are only interested in the program \"init\"..."
echo
echo "We can type"
yellow ; echo
echo "ps aux | egrep \"(init|USER)\" | grep -v grep"
white ; echo
echo "Ah, you haven't seen egrep before! egrep rather usefully lets us look for several things 
at once, as above. Notice the quotes around \"(init|USER)\" - remember special bash characters?"
echo
echo "We add in \"USER\" only to get the headings - we could use any pattern from the heading."
echo
echo "Here is the output..."
echo
ps aux | egrep "(USER|init)" | grep -v grep
echo
echo "Most of the time we won't bother with the headings, and we don't really need to get
rid of the \"grep\" since we know we are running it, so we just run"
echo ; yellow ; echo
echo "ps aux | grep init"
white ; echo
echo "You notice that \"init\" has a PID of 1. It is the process from which all others spring."
echo
echo "Rather than singling out one process, we can look at the way this forest of information
branches from one process to another. There is a --forest option to \"ps\" ! 
	Let's have a look... This is the output of"
echo ; yellow 
echo "ps ax --forest | less"
white ; echo
echo "Hit <space> to see..."

f-tutescape

unbold
ps ax --forest | less 
white ; bold ; echo
echo "The output is a bit difficult to read - you can use a simpler command"
echo ; yellow 
echo "pstree"
echo ; white
echo "Again, if we pipe through \"less\" we can page up and down if needed."
echo
echo "So, try typing below:"
echo ; yellow ; echo
echo "pstree | less"
echo ; white ; unbold
/bin/bash
echo ; bold
echo "Perhaps all this text is starting to bore you... well, here's a colourful alternative
to explore... it updates in real time. In the shell below, type "
yellow ; echo
echo "htop"
white ; echo
echo "q to quit... CTRL+D to return. Have a look at the F-key options in this program..."
unbold ; echo
/bin/bash
clear ; bold ; cyan ; echo
echo "Finding Where Things Live."
white ; echo
echo "A common question asked by beginning users is \"Where does the program go when installed?"
echo
echo "The glib answer is \"Where it's supposed to.\""
echo
echo "The reason for the glib answer is that, at least in Debian-based distributions of GNU/Linux
like Debian, Ubuntu, and of course INX, (which is really Ubuntu underneath), the installation system
sees to this. Unlike some operating systems, Linux-based systems put files for a program in a
number of places. The configuration files tend to go in /etc, and most \"user\" programs have 
their executable binaries in /usr/bin . "
echo
echo "If you need to know where the executable command is, you can find it using these commands:"
echo
yellow 
echo "type"
echo
echo "which"
white ; echo
echo "An example would be"
yellow ; echo
echo "which htop"
echo ; white
echo "Try it here:"
echo ; unbold
/bin/bash
echo ; bold
echo "Now try"
yellow ; bold ; echo
echo "which cd"
white ; echo ; unbold
/bin/bash
echo ; bold
echo "What happened?"
echo
echo "\"cd\" is a shell built-in. The \"which\" command searches your PATH, which is a list of
directories from which you are permitted to run executable programs. So it doesn't find \"cd\" ."
echo 
echo "Now try"
yellow ; echo
echo "type cd"
white ; unbold ; echo
/bin/bash
echo ; bold
echo "The \"type\" command is more general - it will find shell built-ins and commands in 
your PATH as well."
echo "These tricks can be useful as shorthand - for example rather then typing"
echo ; yellow
echo "ls -l /usr/local/bin/playinx"
echo ; white
echo "We can type "
echo ; yellow
echo "ls -l \`which playinx\` "
echo ; white
echo "You will recall that backticks make bash substitute the result of the command within them."
echo "Give it a try:"
unbold ; echo
/bin/bash
echo ; bold
echo "Final screens coming up... aliases and very basic scripting..."

f-tutescape

bold ; cyan ; echo
echo "Also Known As..."
echo ; white 
cat <<EOALIAS
Long commands can be a bore - we want to take advantage of long commands without needing 
to re-type them. There are several ways around this. One is to make an "alias".

This is quite straightforward. Let's take the example of piping "ps aux" through grep.

Let's say you want regular information on all processes being run from /usr/local/bin
(In INX the list is likely to be short enough not to need "less", but this is just an
example).

Rather than constantly typing "ps aux | grep /usr/local/bin | grep -v grep | less" 
we can do this:
EOALIAS

echo ; yellow
echo "alias psl='ps aux | grep /usr/local/bin | grep -v grep | less'"
echo ; white
echo "It's a good idea to check if our alias conflicts with a command first:"
echo ; yellow
echo "type psl"
echo ; white

echo "It doesn't, so we are OK."
echo
echo "Now, each time we type \"psl\", we get the output of the command that
we specified in the \"alias\""
echo
echo "This will only work for one virtual terminal, and until we log out, though. "
echo "On an installed system we could place this alias in our ~/.bashrc file,
so that it would work at all times, since that file is read for every shell, login or not. "
echo
echo "Read ~/.profile , and you will see that it \"sources\" ~/.bashrc"
echo

f-tutescape

echo ; cyan ; bold
echo "Baby Scripts."
echo ; white
echo "An alternative is to fire up an editor like nano, and put our command there as a \"script\"."
echo "We can put it in our PATH - the usual place for locally written scripts is /usr/local/bin ."
echo
echo "You can see your full PATH by typing"
echo ; yellow
echo "echo \$PATH"
echo ; white
echo "Which in INX looks like this (each directory separated by : )"
echo
echo $PATH
echo
echo "So we do:"
echo ; yellow
echo "sudo nano /usr/local/bin/psl"
echo ; white
echo "and write in that file:"
unbold
cat << EOBABYSCRIPT

#!/bin/bash
ps aux | grep /usr/local/bin | grep -v grep | less

EOBABYSCRIPT
bold
echo "then save it, and make it executable with"
echo ; yellow
cat << EOCHMOD
sudo chmod +x /usr/local/bin/psl


EOCHMOD
echo ; white
echo "Now we can use \"psl\" as a shortcut command."
printf "\n\n\n"

bold ; cyan ; echo
echo "That's all for tutorial 6!  Chmod and friends will be explained in tutorial 7."

f-tutescape
f-tutorial
}