Re: Changing $0 after gsub() breaks output

[arnold]

Thanks for the report and easy reproducer. I will work on this.

Arnold

Yasuhiro Yamada <yamada@gr3.ie> wrote:

> Hi.
> Executing gsub() without an action and making changes to $0 will
> corrupt the output.
> This behavior seems like a bug.
>
>     $ ./gawk --version
>     GNU Awk 5.2.1, API 3.2, PMA Avon 8-g1
>     ...
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1'
>     q  <===== broken output
>
> Interestingly, the result is different for each run.
>
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  b0  61  99  0a
>              260   a 231  \n
>     0000004
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  c0  e7  f7  0a
>             300 347 367  \n
>     0000004
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  c0  07  14  0a
>             300  \a 024  \n
>     0000004
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  c0  57  76  0a
>             300   W   v  \n
>     0000004
>
> Older versions do NOT reproduce this issue.
> Also, the outputs are as expected and intuitive.
>
>     $ ./gawk --version
>     GNU Awk 4.1.4, API: 1.1
>     ...
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1'
>     @@@
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  40  40  40  0a
>               @   @   @  \n
>     0000004
>
> This issue seems to occur in v4.2.0 and later.
>
>     $ ./gawk --version
>     GNU Awk 4.2.0, API: 2.0
>     ...
>     $ echo abc | ./gawk 'gsub(".","@") && $0=$1' | od -tx1c
>     0000000  e0  4f  fc  0a
>             340   O 374  \n
>     0000004
>
> My environment is
>
>     $ uname -a
>     Linux ip-172-31-9-222 5.4.0-1093-aws #102~18.04.2-Ubuntu SMP Wed
> Dec 7 00:31:59 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
>     $ gcc --version
>     gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0