Here is one and only conditional statement:

If <expression 1> Then
  ...
ElseIf <expression 2> Then
  ...
Else
  ...
EndIf

In conditions, you can use any valid expression, the result of which is equal to “true” or “false”. For true, a string equal to «1» is taken, for a false - «0» or an empty string.

Unlike expressions in command parameters, an expression in conditions is written without quotes with % sign in front of them:

If %AUTORUN_TCARCH% = 32 Then
  ...
EndIf

If FileExist("%COMMANDER_PATH%\NoClose.exe") Then
  ...
EndIf

Legacy command use

In Autorun before version 2.0.10, only certain special functions could be used in conditions, while the condition was limited to one function. In later versions, this option is left for compatibility.

If [Not] Function1 <parameters> Then
  ...
ElseIf [Not] Function2 <parameters> Then
  ...
Else
  ...
EndIf

It's allowed to use both expressions and function in one condition (but in different branches).