Tcl If else 语句

if {boolean_expression} {
   # statement(s) will execute if the boolean expression is true 
} else {
   # statement(s) will execute if the boolean expression is false
}

#!/usr/bin/tclsh

set a 100

#check the boolean condition 
if {a<20 } {
   #if condition is true then print the following   puts "a is less than 20"
} else {
   #if condition is false then print the following   puts "a is not less than 20"
}
puts "value of a is :a"

a is not less than 20;
value of a is : 100

if {boolean_expression 1} {
   # Executes when the boolean expression 1 is true
} elseif {boolean_expression 2} {
   # Executes when the boolean expression 2 is true 
} elseif {boolean_expression 3} {
   # Executes when the boolean expression 3 is true 
} else {
   # executes when the none of the above condition is true 
}

#!/usr/bin/tclsh

set a 100

#check the boolean condition
if { a == 10 } {
   # if condition is true then print the following   puts "Value of a is 10"
} elseif {a == 20 } {
   # if else if condition is true 
   puts "Value of a is 20"
} elseif { a == 30 } {
   # if else if condition is true   puts "Value of a is 30"
} else {
   # if none of the conditions is true   puts "None of the values is matching"
}

puts "Exact value of a is:a"

None of the values is matching
Exact value of a is: 100