IF

Command: #if {conditional} {commands if true} {commands if false}

         The #if command works similar to an if statement in other languages,
         and is based on the way C handles its conditional statements.
         When an #if command is encountered, the conditional statement is
         evaluated, and if TRUE (any non-zero result) the commands are executed.

         The conditional is evaluated exactly the same as in the #math command,
         if the conditional evaluates as anything except 0 the commands are
         executed. See the 'math' helpfile for more information.

         To handle the case where an if statement is false it can be followed
         by the #else command. Alternatively, the else can be provided as the
         third argument.

Example: #action {%0 gives you %1 gold coins.} {#if {%1 > 5000} {thank %0}}
         If someone gives you more than 5000 coins, thank them.

Example: #alias {k} {#if {"%0" == ""} {kill $target};#else {kill %0}}

Example: #if {"%0" == "{bli|bla}"} {#showme %0 is either bli or bla.}

Related: case, default, else, elseif, math, switch and regexp.