The [dodekalogue%|%rules of Tcl] define three substitutions:  [script
substitution], [variable substitution], and backslash substitution.  



** See Also **

   [double substitution]:   Commands such as `[expr]`, `[eval]`, `[if]`, `[for]`, etc. do their own substitutions, leading to the potential for double substitution.



** Description **

A substtution is a form of '''dynamic [Tcl quoting%|%quoting]''' in which the
value of a substitution is interpolated into a [word] in a [command].  Because
[EIAS%|%Tcl is a string language], substiution plays a prominent role.
Substitution occurs before the the name of the command is read, making it
possible to modify even the name of a command with a substitution:

======
proc p1 {} {
    return {hello from p1}
}

proc p2 {} {
    return {hello from p2}
}

p[incr i] ;# p1 is evaluated
p[incr i] ;# p2 is evaluated
======


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