Bug 257288
| Summary: | awk - loop over array index goes in reverse | ||||||
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| Product: | Base System | Reporter: | parv <parv.0zero9+freebsd> | ||||
| Component: | bin | Assignee: | Warner Losh <imp> | ||||
| Status: | Closed Not A Bug | ||||||
| Severity: | Affects Many People | CC: | imp, parv.0zero9+freebsd | ||||
| Priority: | --- | ||||||
| Version: | 13.0-STABLE | ||||||
| Hardware: | Any | ||||||
| OS: | Any | ||||||
| Attachments: |
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I'll take a closer look, but my first, quick reading of the standard, I see
> in the case of:
> for (variable in array)
> which shall iterate, assigning each index of array to variable in an unspecified order.
From the gawk manual on the for (i in array) construct: "The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array elements within awk and in standard awk cannot be controlled or changed. This can lead to problems if new elements are added to array by statements in the loop body; it is not predictable whether the for loop will reach them. Similarly, changing var inside the loop may produce strange results. It is best to avoid such things." So I think this is a "not a bug" situation. I'll let the originator offer a dissenting view before closing, however. Right. I had suspected that could be one possibility[0]. I had failed to find any blurb related to order of array elements in awk(1) manual page. I had not read the gawk(1) manual page, obviously, as it seemed to have produced desired result at the time. Further testing showed gawk also not producing the ordered output. I will mark this PR to be closed: not a bug. 0- Other rare possibility, by chance, could have been locale interaction; but setting LANG & LC_ALL to "C", & rest to unset, still produced the same result. The text quoted by Warner L about the order of elements is not in gawk(1) manual page , but is present in "info" page ... https://www.gnu.org/software/gawk/manual/gawk.html ... gawk(1) manual page does mention that order could be set by setting 'PROCINFO["sorted_in"]'. I, at this point, would rather pass the output to sort(1); or, not use (any) awk but use perl or python. |
Created attachment 226558 [details] awk on FreeBSD 12, 13 printed lines in reverse order while iterating over array index While trying to print lines with distinct second field in a line to keep only the latest lines with 3 fields, the for-loop goes over the array variable in reverse order surprisingly ... cat <<_LINE | /usr/bin/awk '{ line[$2] = $0 } END { for ( i in line ) { print line[i] } }' 10:09:58 18.1T pool 10:09:59 18.1T pool 10:43:45 18.2T pool 10:43:46 18.2T pool _LINE 10:43:46 18.2T pool 10:09:59 18.1T pool ... I found this behaviour of /usr/bin/awk both on FreeBSD 12.2-RELEASE-p7 & 13-STABLE c 20210628. OTOH, there was no such unexpected surprise from lang/gawk 5.1.0, which printed ... 10:09:59 18.1T pool 10:43:46 18.2T pool Attached is the test shell script.