IEEE Standards Interpretations for IEEE Std 1003.2™-1992 IEEE Standard for Information Technology--Portable Operating System Interfaces (POSIX®)--Part 2: Shell and Utilities
Copyright © 1996 by the Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue New York, New York 10016-5997 USA All Rights Reserved.
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Interpretation Request #48
Topic: Shell parameter expansion Relevant Clauses: Table E-1 Classification: Defect
Please can you indicate whether an error (typographical xor otherwise) has been made in Table E-1 (Volume II, lines 3273-3291 of Annex E) of IEEE Standard 1003.2-1992. Table E-1 seeks to clarify all possible combinations that arise from shell parameter expansions, as described in subclause 3.6.2 of Volume I, lines 399-420. However, if lines 399-417 are read while ignoring the phrase "or null" (as lines 418-420 imply), the resultant table obtained differs from Table E-1 in the following places: Lines 3282,3283; column "parameter set but null": currently: "substitute parameter" should be: "substitute null"
Rationale: The ultimate effect of the operation is the same, since the set parameter has the null value already; however, the proposed change makes this entry more consistent with similar entries of the same column at lines 3278-3279 and 3286-3287. lines 3283,3283; column "parameter unset": currently: "assign null" should be: "assign word"
Rationale: The indicated correction is a direct result of reading subclause 3.6.2, lines 402-404 while ignoring the phrase "or null". It is agreed (lines 3268-3269 of Annex E) that historically this section of documentation has been "hard to understand". The above corrections (if adopted) will help to overcome this difficulty, but the present text only serves to compound the dilemma.
The rationale is in error. Concerns about the wording of this part of the rationale for the standard have been forwarded to the sponsor.
Rationale for Interpretation
Where there is a conflict between the standard and the rationale, the standard takes precedence. It is expected that a future revision of the standard will address this issue.