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Re: [bug-gawk] When RS is null, POSIX states \n should be in FS, gawk on

From: Ed Morton
Subject: Re: [bug-gawk] When RS is null, POSIX states \n should be in FS, gawk only does that if FS is single char
Date: Mon, 15 Apr 2019 09:39:44 -0500
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1

Sounds good, thanks for the quick response.


On 4/15/2019 8:52 AM, address@hidden wrote:

Thanks for the report. This smells like a change in the POSIX
standard, but I will have to research previous standards and also
what the original AWK book says.



Ed Morton <address@hidden> wrote:

I just came across this where setting RS to null causes FS to include
`\n` if FS is a singe char but not otherwise:

     $ printf '1:2\n3\n' | awk -F':' -v RS= '{for (i=1; i<=NF; i++) print
     i"/"NF, "<"$i">"}'
     1/3 <1>
     2/3 <2>
     3/3 <3>

     $ printf '1::2\n3\n' | awk -F'::' -v RS= '{for (i=1; i<=NF; i++)
     print i"/"NF, "<"$i">"}'
     1/2 <1>
     2/2 <2

with this gawk version:

     $ awk --version
     GNU Awk 4.2.1, API: 2.0 (GNU MPFR 4.0.2, GNU MP 6.1.2)
     Copyright (C) 1989, 1991-2018 Free Software Foundation.

and that makes sense given the gawk documentation
(https://www.gnu.org/software/gawk/manual/gawk.html#Multiple-Line) which
says (red/underline mine):

     When RS is set to the empty string _/and /__FS is set to a single
     character_, the newline character always acts as a field separator.
     This is in addition to whatever field separations result from FS^

but the POSIX spec (http://pubs.opengroup.org/onlinepubs/9699919799/) says:

         The first character of the string value of *RS* shall be the
         input record separator; a <newline> by default. If *RS* contains
         more than one character, the results are unspecified. If *RS* is
         null, then records are separated by sequences consisting of a
         <newline> plus one or more blank lines, leading or trailing
         blank lines shall not result in empty records at the beginning
         or end of the input, and a <newline> shall always be a field
         separator, no matter what the value of *FS* is.

gawk behaves the way I described with or without the `--posix` flag.
Shouldn't it add `\n` as a separator when RS is null regardless of the
value of FS like POSIX says? FWIW OSX/BSD awk on MacOS behaves the same
way that gawk does, idk about other awks.

  ???????? Ed.

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