NS-2%20LAB:%20TCL

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NS-2 LAB TCL
Miriam Allalouf

• 2005-2006 - Semester A

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TCL Introduction

• Why Scripting languages?
• C,C,Java ? Perl, Python, TCL
• UNIX scripting languages XTERM shell, PERL
• based around C type language constructs.
• Scripting languages chars.
• Configure
• Glue different application
• Flexible data structure ? easy porting
• Slow but processors power grew!
• Undefined variable types
• Code and Data are the same easy to add code!

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TCL Introduction

• Scripting languages
• A script file is a list of commands which a shell
  interpreter reads and executes.
• First line is a line which indicates what
  interpreter to run.
• Rest of the file is just a sequence of commands,
  most often just like those you can run on your
  command line.
• Script languages include some method for
  manipulating variables and data.

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TCL Introduction

• Script languages TCL
• The tcl interpreter gives a bridging solutions
• TK - display extension for using X widgets
  (TCL/TK)
• XML
• CORBA
• ORACLE, Sybase
• DCOM,SAP,WEB, HTTP
• SNMP
• Test Equipment
• The tcl interpreter is called "tclsh". You can
  run which tclsh
• in order to find out where your tcl interpreter
  is located.
• The first line of your tclsh script should be
• !/your.location/tclsh

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TCL Introduction

• TCL - Tool Command Language - History
• 1980s Tcl invented by John Ousterhout while
  working on design tools for integrated circuits
  at the University of California at Berkeley.
  Wanted a language that could be used over many
  tools.
• To create a good interpreted language
• To build it as a library package that could be
  reused in many different applications.
• To provide a language interpreter with a set of
  generic facilities, such as variables, control
  structures, and procedures.
• To enable the application that used the language
  to extend it and add its own features into the
  language, so that the language could be used to
  control the application.

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TCL Introduction

• TCL Goals
• The goals set for the language were
• The language must be extensible The language
  must be very easy to work on, and it should be
  easy and convenient to add features to the
  language in order to adapt this language to the
  programmers specific goal.
• The application should be very simple and
  generic The application should be able to work
  easily with many different applications in such a
  way that it does not restrict the features that
  those applications have to provide.
• Integration The language should be able to glue
  together the extensions. Thus the language must
  have good facilities for integration.
• The first version of Tcl in a graphical text
  editor was ready by the spring of 1988.
• TCL/Tk Tk was ready by the end of 1990.

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TCL Introduction

• TCL Plan
• Review Tcl syntax
• Expressions
• Lists, arrays
• Strings and pattern matching
• Control structures
• Procedures
• Error handling
• File and network I/O and process management
• Getting info at runtime

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TCL Introduction

• TCL Basics
• Tcl script (String based)
• Sequence of commands.
• Commands separated by newlines, semi-colons.
• Tcl command
• One or more words separated by white space.
• First word is command name, others are arguments.
• Returns string result (always returns usually
  numbers)
• Examples
• set a 22 set the variable a to 22
• puts "Hello, World!" worlds shortest program
• expr 100 20 Calculates the sum of 100 and 20
  and results the result, which is 120

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Division Of Responsibility
TCL Introduction

• Chops commands into words.
• Makes substitutions.
• Does not interpret values of words.
• Single pass operation!

Tcl Parser
Command
Words

• Interprets words.
• Can invoke parser recursively.
• Produces string result.

Command Procedure
Result
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TCL Introduction

• Tcl Tool Command Language
• Simple syntax (similar to sh, C, Lisp)
• set a 47 í 47
• Substitutions
• set b a í 47
• set b expr a10 í 57
• Quoting
• set b "a is a" í a is 47
• set b expr a10 í expr a10

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TCL Introduction

• Variable Substitution
• Syntax varName
• Variable name is letters, digits, underscores.
• This is a little white lie, actually.
• Tcl will promote integers to reals when needed
• All values translated to the same type
• Note that expr knows about types, not Tcl!
• May occur anywhere in a word.
• Sample command Result
• set b 66 66
• set a b b
• set a b 66
• set a bbb 666666
• set a b.3 66.3
• set a b4 no such variable

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TCL Introduction

• Command Substitution
• Syntax script
• Evaluate script, substitute result.
• May occur anywhere within a word.
• Sample command Result
• set b 8 8
• set a expr b2 10
• set a "b-3 is expr b-3" b-3 is 5

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TCL Introduction

• TCL expression
• Whats happening in these expressions?
• expr a cos(2b) ? -5.03443
• a, b substituted by scanner before expr is
  called
• expr b fac 4 ? 120
• here, b is substituted by expr itself
• Therefore, expressions get substituted more than
  once! (In fact, TCL once, and expr once)
• set b \a
• set a 4
• expr b 2 ? 8

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TCL Introduction

• Tcl String Expressions
• Some Tcl operators work on strings too
• set a Bill Bill
• expr a lt "Anne" 0
• lt, gt, lt, gt, , and ! work on strings
• Beware when strings can look like numbers
• You can also use the string compare function

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TCL Introduction

• Controlling Word Structure
• Words break at white space and semi-colons,
  except
• Double quotation marks group words as a single
  argument to a command and prevent breaks.Dollar
  signs and square brackets are interpreted inside
  double quotation marks.
• set a "x is x y is y"
• Curly braces also group words into a single
  argument. In this case, however, elements
  within the braces are not interpreted or
  substituted.
• set a expr bc
• Backslashes quote special characters For
  example, \n generates a newline.
• set a word\ with\ \\ and\ space
• Backslashes can escape newline (continuation)
• Substitutions don't change word structure
• set a "two words"
• set b a

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TCL Introduction

• Notes on Substitution and Parsing
• Tcl substitution rules are simple and absolute
• Example comments
• set a 22 set b 33 lt- OK
• this is a comment lt- OK
• set a 22 same thing? lt- Wrong!
• set a 22 same thing lt- OK
• Parser looks at a command just once!
• Its OK to experiment
• Expressions exist that cant be written in one
  command
• Sometimes things get hairy cmd

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TCL Introduction

• Tcl Commands
• Built-in commands this group of commands is
  provided by the Tcl interpreter itself.
• All of the commands discussed so far.
• Present in all Tcl applications.
• Tcl extension commands created using the Tcl
  extension mechanism.
• Tcl APIs to create a new command where the
  command procedure is implemented in C or C,
  command name be registered with the Tcl
  interpreter. TCL recognizes this particular name
  for a Tcl command and, will execute the new
  command.
• proc commands consists of procedures created
  with the proc command.

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TCL Introduction

• Lists
• Zero or more elements separated by white space
• red green blue
• Braces and backslashes for grouping
• a b c d e f (4 words)
• one\ word two three (3 words)
• List-related commands
• concat lindex llength lsearch
• foreach linsert lrange lsort
• lappend list lreplace
• Note all indices start with 0. end means last
  element

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TCL Introduction

• Lists are Powerful
• Examples
• lindex a b c d e f 2 gt c d e
• lsort red green blue gt blue green red
• A list makes a handy stack
• Sample command Result
• set stack 1 1
• push stack red red 1
• push stack a fish a fish red 1
• pop stack a fish
• (stack contains red 1)
• push and pop are very short and use list commands
  to do their work

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TCL Introduction

• More about Lists
• A true lists meaning wont change when
  (re)scanned
• red animal blue animal lt not a listred fish
  blue fish lt list
• red \fish blue \fish lt not a list, but
• list red \fish blue \fish gives you
• red fish blue fish lt which is a list
• Commands and lists are closely related
• A command is a list
• Use eval to evaluate a list as a command

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TCL Introduction

• String Manipulation
• string subcommands
• compare first last index length
• match range toupper tolower trim
• trimleft trimright
• Note all indexes start with 0. end means last
  char

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TCL Introduction

• Tcl Arrays
• Tcl arrays are 'associative arrays' index is any
  string
• set x(fred) 44
• set x(2) expr x(fred) 6
• array names x
• gt fred 2
• You can 'fake' 2-D arrays
• set A(1,1) 10
• set A(1,2) 11
• array names A
• gt 1,1 1,2 (commas included in names!)

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TCL Introduction

• Control Structures
• C-like in appearance.
• Just commands that take Tcl scripts as arguments.
• Example list reversal. Set list b to reverse of
  list a
• set b ""set i expr llength a - 1while i
  gt 0 lappend b lindex a i incr i
  -1
• Commands
• if for switch break
• foreach while eval continue
• source

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TCL Introduction

• Control Structure Examples
• if expr script
• for script expr script script
• for set i 0 ilt10 incr i ...
• switch (opt) string p1 s1 p2 s2...
• foreach index array names a
• puts a(index)

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TCL Introduction

• More on Control Structures
• Brackets are not required
• set x 3
• if xgt2 ... lt this is OK, evaled once
• while xgt2 ... lt evaled many times!
• set a red blue green
• foreach i a lt this is OK
• foreach i red blue green ...
• 
  NOT OK!
• foreach index array names A is a common idiom

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TCL Introduction

• Procedures
• proc command defines a procedure
• proc sub1 x expr x-1
• Procedures behave just like built-in commands
• sub1 3 í 2
• Arguments can have default values
• proc decr x y 1
• expr x-y
• Return value of a procedure is implicitly the
  return value of the last statement in the script.
  Unless the return command exists.

name
body
list of argument names
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TCL Introduction

• Procedures and Scope
• Scoping local and global variables.
• Interpreter knows variables by their name and
  scope
• Each procedure introduces a new scope
• global procedure makes a global variable local
• gt set x 10
• gt proc deltax d
• set x expr x-d
• gt deltax 1 gt can't read x no such variable
• gt proc deltax d
• global x
• set x expr x-d
• gt deltax 1 gt 9

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TCL Introduction

• Procedures and Scope
• Note that global is an ordinary command
• proc tricky varname
• global varname
• set varname "passing by reference"
• upvar and uplevel let you do more complex things
• level naming
• num 0 is global, 1 is one call deep, 2 is 2
• num 0 is current, 1 is caller, 2 is caller's
  caller
• proc incr varname
• upvar 1 varname var
• set var expr var1

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TCL Introduction

• Procedures and Scope
• uplevel does for code what upvar does for
  variables
• proc loop from to script
• set i from
• while i lt to
• uplevel script
• incr i
• set s ""
• loop 1 5 set s s
• puts s gt

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TCL Introduction

• More about Procedures
• Variable-length argument lists
• proc sum args set s 0
• foreach i args incr s i
  return s
• sum 1 2 3 4 5
• gtgt 15
• sumgtgt 0

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TCL Introduction

• ERRORS
• Errors normally abort commands in progress,
  application displays error message
• set n 0foreach i 1 2 3 4 5 set n expr
  n iií syntax error in expression "n
  ii"
• Global variable errorInfo provides stack trace
• set errorInfoí syntax error in expression "n
  ii" while executing"expr n ii"
  invoked from within"set n expr n ii..."
  ("foreach" body line 2) ...

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TCL Introduction

• Advanced Error Handling
• Global variable errorCode holds machine-readable
  information about errors (e.g. UNIX errno value).
• NONE (in this case)
• Can intercept errors (like exception handling)
• catch expr 2 msgí 1 (catch returns 0OK,
  1err, other values...)
• set msgí syntax error in expression "2 "
• You can generate errors yourself (style
  question)
• error "bad argument"
• return -code error "bad argument"

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TCL Introduction

• Tcl file I/O
• Tcl file I/O commands
• open gets seek flush globclose read tell cd
• fconfigure fblocked fileeventputs source eof pw
  d filename
• File commands use 'tokens' to refer to files
• set f open "myfile.txt" "r"
• ? file4
• puts f "Write this text into file"
• close f

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TCL Introduction

• TCP, Ports, and Sockets Tcl Network I/O
• Tcl provides a simplified Socket library
• socket creates a network connection
• set f socket www.sun.com 80
• fconfigure f -buffering line
• puts f "GET /"
• puts read f
• gt loads of HTML from Sun's home page
• Network looks just like a file!
• To create a server socket, just use
• socket -server accept portno

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TCL Introduction

• I/O and Processes
• exec starts processes, and can use ''
• set FAVORITE_EDITOR emacs
• exec FAVORITE_EDITOR
• no filename expansion use glob instead
• eval exec "ls glob .c"
• you can open pipes using open
• set f open "grep foo bar.tcl" "r"
• while eof f ! 0
• puts gets f

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TCL Introduction

• Runtime Information Facilities
• The info command
• what variables are there?
• info vars, info globals, info locals, info exists
• what procedures have I defined, and how?
• info procs, info args, info default, info body,
  info commands
• the rename command
• can rename any command, even built-in
• can therefore replace any built-in command

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NS-2 lab TCL Introduction

• Resources
• Bibliography The Tcl/Tk track is based  on
  Ousterhout and Welch's book (Practical
  Programming in Tcl/Tk).
• Online resources, some of the  most useful Tcl/Tk
  links  http//dev.scriptics.com/man/tcl8.3/conten
  ts.htm
• Online Tcl/Tk manual pages http//stage.caldera.
  com/Technology/tcl/Tcl.html
• A broad  list of Tcl/Tk resources.
• The Scriptics company (http//www.scriptics.com/)t
  hat commercializes Tcl and its developper web
  site.
• Tutorials
• A  Tcl/Tk introduction
• The  TclTutor
• An online overview with examples.
• Tcl/Tk course material in hebrew (see the lecture
  notes section

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NS-2 lab Introduction

• More Refernces
• http//www.ixiacom.com/products/paa/customappdev/
• http//www.cetus-links.org/oo_tcl_tk.htmloo_tcl_t
  k_start_here
• http//www.pconline.com/erc/tcl.htm
• http//www.scriptics.com/doc/scriptHistory.html
• http//www.itworld.com/AppDev/1243/UIR000804tk/
• http//www.softpanorama.org/Scripting/tcl_tk.shtml
  
• http//www.tcl.tk/advocacy/choose.html
• http//www.cs.utah.edu/dept/old/texinfo/dejagnu/de
  jagnu_8.html
• http//www.usenix.org/publications/library/proceed
  ings/tcl95/
• http//216.239.51.100/search?qcachewTF3fij-gGQC
  www.usenix.org/publications/library/proceedings/tc
  l97/full_papers/poster_bergeman/bergeman-abstract.
  pdftcl/tkapplicationareahlenieUTF-8