Re: Bash parameter expansion (remove largest trailing match, remove largest leading match, pattern replacement) does not work

[Koichi Murase]

2020-08-30 4:54 Bruce Lilly <bruce.lilly@gmail.com>:
> On Sat, Aug 29, 2020, 15:40 Koichi Murase <myoga.murase@gmail.com> wrote:
>> Don't worry.  In this case, the GPL doesn't apply.  Please read the
>> following Q&A.
>>
>> https://www.gnu.org/licenses/gpl-faq.en.html#IfInterpreterIsGPL
>>
>> Even if your original `shellbug' is licensed under something other,
>> and it prohibits to make it public, you can still create another
>> script to reproduce the same issue.  [...]

I'm sorry if I have confused you, but first, let me clarify that I
meant by `create another script' that you can create a completely new
script from scratch instead of extracting the relevant part of the
original script.

> It's a bit more complicated than that; if, for example, some excerpt
> ended up in regression tests, there would be a question about
> whether or not there was a copyright violation.  As I understand the
> GPL (IANAL), it requires all parts of a "work" to be GPL'd, and that
> wouldn't be possible for any parts of the script that ended up in
> bash regression tests.

That's an interesting discussion.  I don't know how you define the
"work", but basically GPL only affects the derivative
programs/software but not all the "work" including the output of the
programs or the knowledge obtained in running/developing the code.

How about thinking in this way: You have gotten the knowledge that the
parameter expansions do not behave as you expected, and that knowledge
is not licensed by GPL.  Then you create a new script from scratch
based on the knowledge by trying to encode the idea directly and not
to be affected by the style of the original script as much as
possible.  I don't know but something like this reduced case:

  text=AABBCC patA='*(A)' patC='+(C)'
  echo "${text##$patA}, ${text%%$patC}"

I believe this shouldn't be considered GPL'd.  Otherwise, anyone who
read a GPL code in the past cannot write any non-GPL programs because
one cannot prove the experience of reading the GPL code doesn't affect
any code that he/she writes thereafter.  I sometimes hear that someone
avoids hiring programmers who have read a GPL code in the past for
defensive purposes, but I believe it's a matter of degree.

2020-08-30 5:07 Bruce Lilly <bruce.lilly@gmail.com>:
> That's surprising, as octal and hexadecimal escapes are fairly
> common.

Yes, I know that it is confusing to those who are familiar with modern
Perl-style regular expressions.  But historically, POSIX regular
expressions do not support the backslash escape sequences in bracket
expressions `[...]'.  The backslash escape sequences in bracket
expressions were the extension historically.  As far as I know, in
POSIX, only awk supports backslash sequences in regular expressions.

> Yes, I'm still looking into that (along with updating a couple of
> FreeBSD machines, eating lunch, and monitoring a couple of
> downloads).  I'll obviously have to wrap the "shopt" bit in a
> wrapper; is there some minimum bash version that supports it?

Bash 2.02 supports `shopt -s extglob', so you can assume every Bash
has the support.  If you are still failing to get an expected
behavior, you can just put the line `shopt -s extglob' in the
beginning of the script.  In the case of the above mentioned reduced
case, you can write like this:

  shopt -s extglob
  text=AABBCC patA='*(A)' patC='+(C)'
  echo "${text##$patA}, ${text%%$patC}"

--
Koichi