Category: TCL

For loop in TCL can be achieved using the command for. It is used to execute code for multiple numbers of time.

Let’s see the syntax of for command:

for { start } { test } { next }

{

body

}

Here, start portion is used to initialise the variable. test is an expression, which will return either true or false . next is the portion to increment a variable, which has been written in the start portion.

Let’s see some examples:

1. Increment by 1

# Example for loop

for {set i 0} {$i < 3} {incr i} {

puts "Value of i is: $i"

}

Output is :

Value of i is: 0
Value of i is: 1
Value of i is: 2

2. Increment by 2

# Example increment by 2

for {set i 0} {$i < 5} {incr i 2} {

puts "Value of i is: $i"

}

Output :

Value of i is: 0
Value of i is: 2
Value of i is: 4

3. Loop through in reverse direction:

# Loop through in reverse direction

for {set i 5} {$i > 0} {incr i -1} {

puts "Value of i is: $i"

}

Output:

Value of i is: 5
Value of i is: 4
Value of i is: 3
Value of i is: 2
Value of i is: 1

Like other programming languages, TCL also provides support to switch case. It is used to test multiple conditions. In TCL switch, we don’t need to write break statement like other languages. To achieve switch case functionality we can also use if else statements .

Let us see syntax of switch case :

switch option switch_expression
switch_expression_1 
{
body_1
}
switch_expression_2
{
body_2
}
switch_expression_3
{
body_3
}
default
{
default_body
}

switch_expression can be a number, alphabet or string . If switch_expression match with any subsequent switch_expressions then body corresponding to that expression will be executed. default block will be executed if switch_expression doesn’t match with any subsequent expressions.

options can be :

-exact : Use exact matching (default)

-glob : When matching string to the patterns like *, ? (i.e. the same as implemented by the string match )

-regexp : When matching string to the patterns, use regular expression.

Let us see some examples :
1. switch case with numbers :

#!/usr/bin/tclsh
set number 5;
switch $number
1 {
puts "One"
}

2 {
puts "Two"
}

3 {
puts "Three"
}

default {
puts "Invalid Number."
}
}

#!/usr/bin/tclsh
set country_code "US";
switch $country_code {
US {
 puts "United States of America"
}
IN {
 puts "India"
}
UK {
 puts "United Kingdom"
}
default {
 puts "Invalid Country Code"
}
}

#!/usr/bin/tclsh
set var_string computer;

switch -glob $var_string {
com*er {
 puts "Matched with com*er"
 }
default {
 puts "Invalid !"
 }
}

Output:
$tclsh main.tcl
Matched with com*er

We are  adding comments in source code to make it easier to understand or we can also use comments to add legal notices, like copyrights or to add some TODOs, Author name etc.

In TCL, we can add comments in three ways .

1. Complete Line Comments:

For complete line comments, we need to use # sign in beginning. For example

# This line is commented...
puts "Hello World!"

2. Inline Comments:

Sometimes we need to write a comment just after finishing our code on the same line. In such cases, we can use inline comments.  Inline comments start with ;# in line. For example :

puts $tcl_version ;# This will print TCL Version

3. Block Comments:

Sometimes we need to add comments to the block of line or to the complete procedure. In such case, we can use block comments. We need to use if with condition 0 for block comments. For example :

puts "This line is not commented !"

if 0 {

This is an example of multi-line comments.

This complete block will be considered as comments.

}

puts "Even this is not comment"

Try to use these types of comments in TCL scripts !