Answering questions that may arise related to the meaning of portions of an IEEE standard concerning specific applications.

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 #151
Topic: pr Relevant Clauses: 4.49.3

This request deals with the semantics of the "-i" option to the "pr" utility. These semantics are specified in POSIX.2 subclause 4.49.3 lines 8037-8043, which state (in part): -i[char][gap] In output, replace multiple s with s wherever two or more adjacent s reach column positions gap + 1, 2 x gap + 1, 3 x gap + 1, etc. If gap is zero or is omitted, default settings at every eighth column position shall be assumed. The issue that I would like addressed is the following: If an input line contains a space at position (n x gap + 1) followed by n consecutive spaces, should the output file contain a single space at position (n x gap + 1) followed by a single tab, or should it contain two tabs? An example may make this clearer. Suppose that "inputfile" contains the following two lines 1234567890 This line shows column positions 123 90 (five consecutive spaces, no tabs, in the second line) and suppose that the command pr -i4 inputfile is issued. Should the output generated by the second line be 123 ^I90 or 123^I^I90 >Here ^I stands for a tab. I contend that the second output is correct (or that, at best, the standard is ambiguous). To support this, note that the five consecutive spaces reach column position 9 = (2 x 4 + 1), and therefore (according to the specification) should all be replaced by tabs. The fact that the first of these spaces is at a tab position does not seem relevant and is not addressed in the standard.

Interpretation Response
The standard is clear. The five s should be replaced by two s. However, while reviewing this interpretation request, we note that historical implementations would replace one or more s with the appropriate number of s. This issue has been forwarded to the sponsors.

Rationale for Interpretation