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cond-token-var.mk revision 1.6 
      1 # $NetBSD: cond-token-var.mk,v 1.6 2021/04/25 21:05:38 rillig Exp $
      2 #
      3 # Tests for variable expressions in .if conditions.
      4 #
      5 # Note the fine distinction between a variable and a variable expression.
      6 # A variable has a name and a value.  To access the value, one writes a
      7 # variable expression of the form ${VAR}.  This is a simple variable
      8 # expression.  Variable expressions can get more complicated by adding
      9 # variable modifiers such as in ${VAR:Mpattern}.
     10 #
     11 # XXX: Strictly speaking, variable modifiers should be called expression
     12 # modifiers instead since they only modify the expression, not the variable.
     13 # Well, except for the assignment modifiers, these do indeed change the value
     14 # of the variable.
     15 
     16 DEF=	defined
     17 
     18 # A defined variable may appear on either side of the comparison.
     19 .if ${DEF} == ${DEF}
     20 .  info ok
     21 .else
     22 .  error
     23 .endif
     24 
     25 # A variable that appears on the left-hand side must be defined.
     26 # The following line thus generates a parse error.
     27 .if ${UNDEF} == ${DEF}
     28 .  error
     29 .endif
     30 
     31 # A variable that appears on the right-hand side must be defined.
     32 # The following line thus generates a parse error.
     33 .if ${DEF} == ${UNDEF}
     34 .  error
     35 .endif
     36 
     37 # A defined variable may appear as an expression of its own.
     38 .if ${DEF}
     39 .endif
     40 
     41 # An undefined variable on its own generates a parse error.
     42 .if ${UNDEF}
     43 .endif
     44 
     45 # The :U modifier turns an undefined expression into a defined expression.
     46 # Since the expression is defined now, it doesn't generate any parse error.
     47 .if ${UNDEF:U}
     48 .endif
     49 
     50 # If the value of the variable expression is a number, it is compared against
     51 # zero.
     52 .if ${:U0}
     53 .  error
     54 .endif
     55 .if !${:U1}
     56 .  error
     57 .endif
     58 
     59 # If the value of the variable expression is not a number, any non-empty
     60 # value evaluates to true, even if there is only whitespace.
     61 .if ${:U}
     62 .  error
     63 .endif
     64 .if !${:U }
     65 .  error
     66 .endif
     67 .if !${:Uanything}
     68 .  error
     69 .endif
     70