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An Introduction To TclScripting

SESSION - 1

- Akhilesh Mahajan

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Todays Agenda

Why TCL? TCL Commands

Variables Declaration

Substitution

Basics of Lists

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Why TCL?

Simplicity

GUI

Development Tools

Internationalization

Extensibility

Embed ability

Compatibility

Event Handling

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Comparison Chart

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Getting Started Tcl programs are usually called "scripts"

The binaries and libraries of Tcl/Tk and its

extensions are generally installed under /usr/bin

and /usr/lib.

You need to set up a few environment variables

in your .cshrc/.bashrc

setenv TCL_LIBRARY ~/tcl/itcl/lib/tcl7.4

setenv TK_LIBRARY ~/tcl/itcl/lib/tk4.0setenv ITCL_LIBRARY ~/tcl/itcl/lib/itcl2.0

setenv ITK_LIBRARY ~/tcl/itcl/lib/itk2.0

setenv EXPECT_LIBRARY ~/tcl/expect/lib

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TCL Commands

Built-in Commands

Extensions

Procedures

Parser

Init

CommandLoop

ApplicationCommands

Built-InCommands

Tcl Application

ExtensionCommands

Extension

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Variable Declaration

Set varName ?value?

e.g. set x 40

Same command is use to Read and Write You don't need to declare variables

Variables created automatically

Variables do not have typesAny variable can hold any value

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Variable Declaration (Cont.)

Other Examples:set a {Eggs: $3.5/dozen}Eggs: $3.5/dozen

set i 3

set a [expr $i + 2]5

set msg Starent Networks

Starent Networks

Unset a Variable

unset ?varname?

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Substitution

TCL provides THREE types ofsubstitution

1. Variable Substitution2. Command Substitution

3. Backslash Substitution

Substitution always occurs from left toright

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Variable Substitution

Syntax: $varName

Variable names are letters, digits, underscores.

May occur anywhere in a word.

Sample command Result

set b 66 66set a b bset a $b 66

set a $b+$b+$b 66+66+66set a $b.3 66.3set a $b4 no such var iable

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Command Substitution

Syntax: [scr ip t]

Evaluate script, substitute result.

May occur anywhere within a word.

Sample command Result

set b 8 8

set a [expr $b+2] 10set a "b-3 is [expr $b-3]" b-3 is 5

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Backslash Substitution

Used to insert special characters such as

newline

[ ]

$

without them being treated specially by TCL

parser.

set msg Eggs:\ \$2.18/dozen\nGasoline:\\$1.49/gallon

Eggs: $2.18/dozen

Gasoline: $1.49/gallon

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Quoting

Words break at white space and semi-colons, except:

Double-quotes prevent breaks:set a "x is $x; y is $y"

Curly braces prevent breaks and substitutions:set a {[expr $b*$c]}

Backslashes quote special characters:set a word\ with\ \$\ and\ space

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Expressions expr arg ?arg arg ...?

Concatenates all the arg values together (with spaces inbetween), evaluates the result as an expression, and returns

a string corresponding to the expressions value.

Sample command Resultset b 5 5incr b -1 4expr ($b*4) - 3 17

expr $b

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Operators

Available Operators:

Arithmetic Operators

Relational Operators

Logical Operators

Bitwise Operators

Choice Operators

Identical to C, C++, Java.

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List Lists are used in Tcl to deal with collections of things

1. such as all the users in a group or

2. all the files in a directory

Lists allow you to collect together anynumber of values in one place, pass

around the collection as a single entity,

and later get the component values back

again

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Creating ListFour ways to create a list

Set x {a b c d e} or

Set y a b c d e or

Set z [list a b c d e]Set x [concat $x $y $z]

concatremoves one level of grouping beforeforming the list, while listworks directly from

the original arguments

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List and Concat

The command

lista b "c d e " " f {g h}"

will returna b {c d e } { f {g h}}

while concatwith the same arguments will

returna b c d e f {g h}

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Split and Join

Split a string into a proper Tcl list

Join create a string by joining list elementstogether

Set dir /usr/bin/radius

Set abc [Split $dir /]

usr bin radius

Set abc [join $abc ;]

usr;bin;radius

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Operation on List

lappend

lindex

linsert

llength

lrange

lreplace

lsearch

lsort

lrepeat