Custom Commands

Also known as procedure.

Syntax: Definition-

proc procName {list_of_params} {

   ## Procedure body

}

Invoke-

procName [ args ... ]

Do not use parenthesis around args while invoking a procedure, since it is a command not a function.

Return variable is optional in procedure definition

In face, return command is also optional.

Example:

% proc message {} {
    puts "Inside message proc."
 }

% message
Inside message proc.

* Local variables defined inside a procedure are accessible only to that procedure.
* Variables defined outside the procedure cannot be accessed directly by the procedure.

Default arguments:
% proc message { {a 1} {b 2} } {
    puts "Inside message proc with a=$a, b=$b"
 }

% message 

Inside message proc with a=1, b=2

% message 4

Inside message proc with a=4, b=2

% message 5 6

Inside message proc with a=5, b=6

Note: If at all default arguments are present for a procedure, the last argument should a default argument.

To access variables defined in script inside a procedure use global:

proc add {} {
    global a b
    return a+b
}
set a 4
set b 1
puts [ add  ]

5


To access variables defined inside caller procedure:

proc proc3 {} {
   upvar 1 x w y v z u
   upvar 2 b z
   puts "Inside proc3: Values from proc2 x=$w y=$v z=$u"
   puts "Inside proc3: Values from proc1 b=$z"

}

proc proc2 {} {
   upvar 1 a x b y
   upvar 2 b z
   puts "Inside proc2: Values from proc1 a=$x b=$y"
   puts "Inside proc2: Values from script b=$z"
   set x 12
   set y 17

   set z 22
   proc3

}

proc proc1 {} {
   set a 100
   set b 99
   proc2
}

set b 20
proc1


Inside proc2: Values from proc1 a=100 b=99
Inside proc2: Values from script b=20
Inside proc3: Values from proc2 x=12 y=17 z=22

Inside proc3: Values from proc1 b=99

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