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var-op-assign.mk revision 1.6 
      1 # $NetBSD: var-op-assign.mk,v 1.6 2020/10/24 08:50:17 rillig Exp $
      2 #
      3 # Tests for the = variable assignment operator, which overwrites an existing
      4 # variable or creates it.
      5 
      6 # This is a simple variable assignment.
      7 # To the left of the assignment operator '=' there is the variable name,
      8 # and to the right is the variable value.
      9 #
     10 VAR=	value
     11 
     12 # This condition demonstrates that whitespace around the assignment operator
     13 # is discarded.  Otherwise the value would start with a single tab.
     14 #
     15 .if ${VAR} != "value"
     16 .  error
     17 .endif
     18 
     19 # Whitespace to the left of the assignment operator is ignored as well.
     20 # The variable value can contain arbitrary characters.
     21 #
     22 # The '#' needs to be escaped with a backslash, this happens in a very
     23 # early stage of parsing and applies to all line types, except for the
     24 # commands, which are indented with a tab.
     25 #
     26 # The '$' needs to be escaped with another '$', otherwise it would refer to
     27 # another variable.
     28 #
     29 VAR=	new value and \# some $$ special characters	# comment
     30 
     31 # When a string literal appears in a condition, the escaping rules are
     32 # different.  Run make with the -dc option to see the details.
     33 .if ${VAR} != "new value and \# some \$ special characters"
     34 .  error ${VAR}
     35 .endif
     36 
     37 # The variable value may contain references to other variables.
     38 # In this example, the reference is to the variable with the empty name,
     39 # which always expands to an empty string.  This alone would not produce
     40 # any side-effects, therefore the variable has a :!...! modifier that
     41 # executes a shell command.
     42 VAR=	${:! echo 'not yet evaluated' 1>&2 !}
     43 VAR=	${:! echo 'this will be evaluated later' 1>&2 !}
     44 
     45 # Now force the variable to be evaluated.
     46 # This outputs the line to stderr.
     47 .if ${VAR}
     48 .endif
     49 
     50 # In a variable assignment, the variable name must consist of a single word.
     51 #
     52 VARIABLE NAME=	variable value
     53 
     54 # But if the whitespace appears inside parentheses or braces, everything is
     55 # fine.
     56 #
     57 # XXX: This was not an intentional decision, as variable names typically
     58 # neither contain parentheses nor braces.  This is only a side-effect from
     59 # the implementation of the parser, which cheats when parsing a variable
     60 # name.  It only counts parentheses and braces instead of properly parsing
     61 # nested variable expressions such as VAR.${param}.
     62 #
     63 VAR(spaces in parentheses)=	()
     64 VAR{spaces in braces}=		{}
     65 
     66 # Be careful and use indirect variable names here, to prevent accidentally
     67 # accepting the test in case the parser just uses "VAR" as the variable name,
     68 # ignoring all the rest.
     69 #
     70 VARNAME_PAREN=	VAR(spaces in parentheses)
     71 VARNAME_BRACES=	VAR{spaces in braces}
     72 
     73 .if ${${VARNAME_PAREN}} != "()"
     74 .  error
     75 .endif
     76 
     77 .if ${${VARNAME_BRACES}} != "{}"
     78 .  error
     79 .endif
     80 
     81 # In safe mode, parsing would stop immediately after the "VARIABLE NAME="
     82 # line, since any commands run after that are probably working with
     83 # unexpected variable values.
     84 #
     85 # Therefore, just output an info message.
     86 .info Parsing still continues until here.
     87 
     88 all:
     89 	@:;
     90