Geoff Clare <g...@opengroup.org> wrote, on 10 Aug 2018: > > Robert Elz <k...@munnari.oz.au> wrote, on 10 Aug 2018: > > > > set --; A=; for x in a $A b $* c; do printf "[%s]\n" "$x"; done > > > > needs to produce > > > > [a] > > [b] > > [c] [...] > > A=: ; IFS=: ; for x in a $A b; do printf "[%s]\n" "$x"; done > > needs to produce > > [a] > > [] > > [b]
> The best way forward might be for someone familiar with the source > of ksh93 or bash (or another popular shell) to look at how the shell > actually decides whether the complete expansion produces nothing or > a single empty field. > > It may be that the place to document it is not in 2.6 but in one > of the individual expansions (e.g. Field Splitting), so for now > I'll leave bugnote 4082 saying to delete it. Actually, I think the existing description of Field Splitting handles it correctly. It may be easier to see if you consider: set --; A=" "; for x in a $A b $* c; do printf "[%s]\n" "$x"; done Applying "any sequence of <space>, <tab>, or <newline> characters at the beginning or end of the input shall be ignored and any sequence of those characters within the input shall delimit a field" to $A (after parameter expansion) results in the space characters being ignored, and then there are no non-IFS characters left to constitute a field, and no IFS characters left to delimit a field, so the result is no fields. (The $* isn't an issue because parameter expansion produces "one field for each positional parameter that is set". There are no positional parameters set, so there are no fields.) With: A=: ; IFS=: ; for x in a $A b; do printf "[%s]\n" "$x"; done applying "Each occurrence in the input of an IFS character that is not IFS white space, along with any adjacent IFS white space, shall delimit a field" results in the ':' delimiting (terminating) a field and thus the result is one empty field. So I think just deleting that paragraph, as bugnote 4082 currently has it, is the right thing to do. -- Geoff Clare <g.cl...@opengroup.org> The Open Group, Apex Plaza, Forbury Road, Reading, RG1 1AX, England
