POSIX.1-2008 added a new sentence to the description of uniq: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/uniq.html
> [...] The trailing <newline> of each line in the input shall be > ignored when doing comparisons. It comes from this interpretation: https://collaboration.opengroup.org/austin/interps/documents/14355/AI-133.txt POSIX.1-2001 doesn't have this sentence: https://pubs.opengroup.org/onlinepubs/009695399/utilities/uniq.html This distinction changes behavior slightly. My interpretation is that the last line in the input can be a duplicate of the penultimate line even if said last line is missing the terminating newline byte. Consider a practical example. Here is -current uniq(1): $ printf "line\nline" | uniq -c 1 line 1 line$ (note that we do not append the missing newline to the output and my shell prompt is printed on the same line.) Here is uniq(1) with my patch: $ printf "line\nline" | obj/uniq -c 2 line Do we want this? On the one hand, it is intuitive that two buffers are not literally the same if one has a newline and the other does not. strcmp(3) agrees with this. ... On the other hand, it also seems intuitive that two records are the same even if one record doesn't have a record delimiter. You could argue that this makes the utility more flexible in a small corner case. Thoughts? Of note is that we already claim conformance to POSIX.1-2008 in the uniq.1 manpage even though we are missing this behavior. This is the only major behavior change inttroduced between POSIX.1-2001 and POSIX.1-2008. If we decide not to add this behavior I think we should dial back the standard quoted in the manpage to POSIX.1-2001. FWIW, GNU uniq implements this behavior: $ printf "line\nline" | guniq 2 line As does FreeBSD, since 2002, although they don't mention it in their manpage. Here's the commit: https://cgit.freebsd.org/src/commit/usr.bin/uniq/uniq.c?id=4e774f7fbe7c154f101f90c115b702780920ebcb Index: uniq.c =================================================================== RCS file: /cvs/src/usr.bin/uniq/uniq.c,v retrieving revision 1.28 diff -u -p -r1.28 uniq.c --- uniq.c 1 Nov 2021 23:20:35 -0000 1.28 +++ uniq.c 2 Nov 2021 01:16:52 -0000 @@ -49,7 +49,7 @@ int cflag, dflag, iflag, uflag; int numchars, numfields, repeats; FILE *file(char *, char *); -void show(FILE *, char *); +void show(FILE *, char *, int); char *skip(char *); void obsolete(char *[]); __dead void usage(void); @@ -60,7 +60,8 @@ main(int argc, char *argv[]) char *prevline, *t1, *t2, *thisline; FILE *ifp = NULL, *ofp = NULL; size_t prevsize, thissize, tmpsize; - int ch; + ssize_t len; + int ch, prevnl, thisnl; setlocale(LC_CTYPE, ""); @@ -133,16 +134,22 @@ main(int argc, char *argv[]) prevsize = 0; prevline = NULL; - if (getline(&prevline, &prevsize, ifp) == -1) { + if ((len = getline(&prevline, &prevsize, ifp)) == -1) { free(prevline); if (ferror(ifp)) err(1, "getline"); exit(0); } + prevnl = prevline[len - 1] == '\n'; + if (prevnl) + prevline[len - 1] = '\0'; thissize = 0; thisline = NULL; - while (getline(&thisline, &thissize, ifp) != -1) { + while ((len = getline(&thisline, &thissize, ifp)) != -1) { + thisnl = thisline[len - 1] == '\n'; + if (thisnl) + thisline[len - 1] = '\0'; /* If requested get the chosen fields + character offsets. */ if (numfields || numchars) { t1 = skip(thisline); @@ -154,13 +161,14 @@ main(int argc, char *argv[]) /* If different, print; set previous to new value. */ if ((iflag ? strcasecmp : strcmp)(t1, t2)) { - show(ofp, prevline); + show(ofp, prevline, prevnl); t1 = prevline; prevline = thisline; thisline = t1; tmpsize = prevsize; prevsize = thissize; thissize = tmpsize; + prevnl = thisnl; repeats = 0; } else ++repeats; @@ -169,7 +177,7 @@ main(int argc, char *argv[]) if (ferror(ifp)) err(1, "getline"); - show(ofp, prevline); + show(ofp, prevline, prevnl); free(prevline); exit(0); @@ -181,13 +189,15 @@ main(int argc, char *argv[]) * of the line. */ void -show(FILE *ofp, char *str) +show(FILE *ofp, char *str, int newline) { if ((dflag && repeats) || (uflag && !repeats)) { if (cflag) (void)fprintf(ofp, "%4d %s", repeats + 1, str); else (void)fprintf(ofp, "%s", str); + if (newline) + fputc('\n', ofp); } }
