If - Else If - Else - EndIf

if expression then

       …

else if expression then

       …

else

       …

endif

These statements allow conditional execution of FISH code segments; else and else if are optional, and the word then may be omitted if desired.

The expression following if or else if may be any expression that evaluates to a boolean, or has a type that will convert to a boolean after evaluation. For example, an integer result will be considered false if it is 0 and true if it has any non-zero value.

if … else if … else … endif clauses can be nested to any depth.

As a special case shorthand, a FISH expression or function list may follow the then keyword in the following syntax

if expression then expression

This allows simple conditions to be expressed in a single line, for example:

if x<0.0 then system.error = "this is an error"

If the shorthand syntax is used else and else if statements are not allowed, and the then keyword is required.