Re: difference in RS handling for equivalent regexps with unending input stream

[Ed Morton]

It seems like there's an additional couple of issues here. If we don't 
have some other character (e.g. newline in my original example but could 
be any other character) after the final `|;`| then the output is a 
record behind the input even with the bracket expression regexp which 
works best:

|$ printf 'A;B;C;' > file $ cat file - | awk -v RS='(;|=)' '{print $0; 
fflush()}' $ cat file - | awk -v RS=';|=' '{print $0; fflush()}' A $ cat 
file - | awk -v RS='[;=]' '{print $0; fflush()}' A B |

and if we change the |RS| to add an additional possible separator to the 
bracket expression we get this very odd behavior:

|$ cat file - | awk -v RS='[;|=]' '{print $0; fflush()}' A $ cat file - 
| awk -v RS='[;a=]' '{print $0; fflush()}' A B C |


On 7/3/2024 4:10 AM, Ed Morton wrote:
> Configuration Information [Automatically generated, do not change]:
> Machine: x86_64
> OS: cygwin
> Compiler: gcc
> Compilation CFLAGS: -ggdb -O2 -pipe -Wall -Werror=format-security 
> -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-strong 
> --param=ssp-buffer-size=4 
> -fdebug-prefix-map=/cygdrive/d/a/scallywag/gawk/gawk-5.3.0-1.x86_64/build=/usr/src/debug/gawk-5.3.0-1 
> -fdebug-prefix-map=/cygdrive/d/a/scallywag/gawk/gawk-5.3.0-1.x86_64/src/gawk-5.3.0=/usr/src/debug/gawk-5.3.0-1 
> -DNDEBUG
> uname output: CYGWIN_NT-10.0-22631 TournaMart_2023 3.5.3-1.x86_64 
> 2024-04-03 17:25 UTC x86_64 Cygwin
> Machine Type: x86_64-pc-cygwin
>
> Gawk Version: 5.3.0
>
> Attestation 1:
>         I have read 
> https://www.gnu.org/software/gawk/manual/html_node/Bugs.html.
>         Yes
>
> Attestation 2:
>         I have not modified the sources before building gawk.
>         True
>
> Description:
>
>    Someone asked a question on SO about handling unending input from
>    netcat with a regexp delimiter that's just 2 possible chars, see
> https://stackoverflow.com/q/78700014/1745001, where gawk seems to be
>    a record behind in it's processing. I'm using bash on cygwin, they
>    used zsh on MacOS.
>
> Repeat-By:
>
>    I can reproduce the problem with this (hitting control-C to stop
>    each command when it stops to wait for more input):
>
>    $ printf 'A;B;C;\n' > file
>
>    $ cat file - | awk -v RS='(;|=)' '{print NR, $0}'
>    1 A
>
>    $ cat file - | awk -v RS=';|=' '{print NR, $0}'
>    1 A
>    2 B
>
>    $ cat file - | awk -v RS='[;=]' '{print NR, $0}'
>    1 A
>    2 B
>    3 C
>
>    Obviously that's 3 supposedly equivalent regexps producing 3
>    different results.