Interpretations

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 #136
Topic: fc -l Relevant Sections: 5.12.4

Historical shells do not implement fc -l as described in IEEE Std 1003.2-1992 since they include the current "fc" call in the output. Was this change from historical behavior intentional ? On page 546, section 5.12.4, lines 2196-2197 specify that "if last is omitted, last shall default to the previous command when -l is specified". It's clear that "previous command" refers to the command immediately preceding the "fc" call from lines 2198-2200, as it would make no sense to edit only the fc call. Historical Korn Shell behavior with -l when last was not specified was to display everying including the current fc command (or whatever command caused fc to be invoked). This means that the description in the standard is not consistant with historical practice. In addition, with historical practice, the 16 commands included the current command so that only the 15 previous commands are displayed.

Interpretation Response
The standard is unclear on this issue, and as such no conformance distinction can be made between alternative implementations based on this. This is being referred to the sponsor. There is no clear definition of whether the previous command refers to the history before fc was entered or the history including the fc command. It also appears that in historic practice this definition varied depending on the options given.

Rationale for Interpretation
None.