From: Hossam Abbas (habbas97@yahoo.com)
Date: Tue Mar 20 2007 - 18:32:54 ART
Hi Olayemi,
I don't know what to say, but i think i will save ur mail as a
reference for me, i know u take a large bite from ur time to write this mail
and try to explain to me TCL script language in such a very easy and smooth,
step by step to help me understand this issue, which i grantee to u that u
succeeded
i don't know what to say but i really thank u for ur help, ur very
nice explanation, and of course ur time
see u soon in another question
----- Original Message ----
From: "Salau,Olayemi"
<Olayemi.Salau@southampton.gov.uk>
To: Hossam Abbas <habbas97@yahoo.com>;
Cisco certification <ccielab@groupstudy.com>
Cc: Olayemi Salau
<salauolayemi@yahoo.co.uk>
Sent: Tuesday, March 20, 2007 7:48:39 PM
Subject:
RE: TCL Script
Hello Hossam,
Don't know if you're conversant with shell
scripts, but this is no different at all, just basic programming logic.
The
Cisco IOS on routers have got an inbuilt shell called tclshell, based on the
tool control language. This is just like any other programming language,
with the aid of a shell prompt called tclshell, you can interact with the
router using the tcl programming language.
Just like using command.exe to
interact with DOS based systems, or sh/ksh/csh/ash/bash to interact with
unix-based OSes.
Also, internetworkexpert provided a good intro into this:
have a look: http://www.internetworkexpert.com/resources/tclshrsh.htm
I
guess the above gives a good intro about shells, now lets move on to the
command basics:-
In any programming language, there are so many things to
talk about, but you only need a few of them in CCIE Lab:
- Variables
-
Procedures
- Expressions
- Loop
- Strings
- A few
other bits
You can find a link to a good tutorial here:
http://www.tcl.tk/man/tcl8.5/tutorial/tcltutorial.html
But I will try to
explain the commands you sent across:
Tclsh <<<<<< This activates or take
you to the shell where you can start your tcl programming
foreach i {
<<<<<<<< The foreach statement starts a loop where you need to do some things
with some objects, this
will keep reoccurring until the process jumps out of
a loop.
Analogy:- Youve got 5 kids and need to buy them all sweets, so youll
need to do the buying 5 times i.e kid A, kid B, kid C, kid D and Kid E
Also, when you do a loop, you dont just do if for fun, youll have to specify
an action to follow.
The i on the line above could be seen as a variable,
something that changes within the loop, a widely used analogy in the
programming world would be a cup, which can be filled with different kind of
liquids, water, orange juice, fanta, or even BEER J. But to be consistent with
the analogy I used about the kids, the content of this Cup would be the Kids
i.e. A, B, C, D and E.
So the next line is where you declare your values,
i.e. the value that the cup contains within a turn of the loop, in your
example, the loop will go round 3 times. In my own analogy about the kids, it
will go round 5 times. So for me, what I would do here is put in my five
values Kid A, Kid B etc.
136.1.136.1
136.1.15.1
150.1.1.1
} { puts [
exec ping $i ] } <<<<<< this line is the tricky bit I guess, but lets keep
things simple, lets say this
is the line where you declare what you want to
output to the screen
Now in the Cisco world, to ping, you need to execute a
command e.g. ping 1.1.1.1 on the Routers prompt. In the real world, you
type with your keyboard to input these xters into your execution prompts, In
TCL programming, what does this is exec.
The command you want to execute
is ping something, Hence in double qoutes.
Now remember what is important
to us is the content of the cup but not the cup itself, so whats important to
us will be $i and not i itself. The content of variable i is the something
we want to ping
Im not sure if youve got the grips you need on this, but
the link I provided explains what the difference is between using ,[], and
() in tcl programming. My own aim is just to throw a sort of introductory
light on tcl programming.
These are used to output characters with
option to substitute contents of variable
{} These are used to output
characters without option to substitute contents of variables, ie. What you
enclose here is exactly what is printed on the screen. So if I do puts {$i};
you will get $i on the screen as opposed to the content of i
[] These are
used to execute commands, see it as a subprocedure/subroutine kind of thing
where the output of a command in fed as input to another command
Also
remember that all of your commands can go in one line, but we tend to use the
enter key after each variable for best practice:
foreach i { 136.1.136.1
136.1.15.1 150.1.1.1 } { puts [exec ping $i] }
The above will achieve the
same result.
Hope this helps, Im closing for the day at work now. Dont
forget this link for futher details:
http://www.tcl.tk/man/tcl8.5/tutorial/tcltutorial.html
Many Thanks
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