IEEE Standards Interpretations for IEEE Std 1003.2™-1992 IEEE Standard for Information Technology--Portable Operating System Interfaces (POSIX®)--Part 2: Shell and Utilities
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Interpretation Request #113
Topic: $< macro evaluation Relevant Clauses: 18.104.22.168
Subclause 22.214.171.124 states, lines 607-610: In an inference rule, the $< macro shall evaluate to the file name whose existence allowed the inference rule to be chosen for the target. In the .DEFAULT rule, the $< macro shall evaluate to the current target name. The $< macro shall be evaluated only for inference rules. What does it mean to "be evaluated only for inference rules" ? There seems to be a contradiction since the 2nd last sentence describes the behaviour for the .DEFAULT rule, but .DEFAULT is not an inference rule. How should one interpret this apparent contradiction? What happens to $< in rules that are not inference or .DEFAULT? Should $< remain a literal string (e.g "$<" ) or should it be treated as an empty string "" (as is done in some historical makes) or are alternate implementation defined behaviours allowed (e.g some non-USL based makes, such as from MKS and GNU, substitutes $< to be the list of all the prerequisites) Thank you for your attention to this matter.
As has been pointed out, the standard contains a contradiction for the $< macro and no conformance distinction can be made between alternative implementations based on this. This is being referred to the sponsor.
Rationale for Interpretation