if ';' STRING ';' STRING ( ';' STRING )?

if         ::= 'if' ';' condition ';' expansion ( ';' expansion )?
condition  ::= true | false
false      ::= 'false' | ''
true       ::= ! false
expansion  ::= ...

The ${if} macro allows a conditional expansion. The first argument is the condition. the condition is either false (empty or ‘false’) or otherwise true. If the condition is true, the value of the macro is the second argument, the first expansion. Otherwise, if a third argument is specified this is returned. If no third argument is specified, an empty string is returned.

Examples

# expands to 'B'
aorb = ${if;;A;B}

# Display ${foo} if set, otherwise 'Ouch'. See also ${def} 
whatisfoo = ${if;${foo};${foo};Ouch}

# Include a file conditionally
-include ${if;${test};test.bnd}