Re: string substitution broken since 5.2

[Alex fxmbsw7 Ratchev]

On Fri, Nov 4, 2022, 17:03 Greg Wooledge <greg@wooledge.org> wrote:

> On Fri, Nov 04, 2022 at 01:30:16PM +0100, Alex fxmbsw7 Ratchev wrote:
> > > 1) Put something like "shopt -u patsub_replacement 2>/dev/null || true"
> > >    at the top of your script.
> > >
> >
> > there d be many such senselessnesses
> >
> > >
> > > 2) Assign the result of the expansion to a temporary variable, and pass
> > >    the temp var to somecmd.  Every.  Single.  Time.
> > >
> >
> > ? i dont get that
>
> OK.  Let me offer a quick example script.  It works as expected in
> bash-5.1:
>
> unicorn:~$ cat foo
> #!/bin/bash
> template='The best candy is clearly @CANDY@!'
> candy='M&Ms'
> printf '%s\n' "${template/@CANDY@/"$candy"}"
>
> unicorn:~$ ./foo
> The best candy is clearly M&Ms!
>
> Now, let's run this script under bash-4.2:
>
> unicorn:~$ bash-4.2 ./foo
> The best candy is clearly "M&Ms"!
>
> Uh oh!  The quotes are wrong for bash-4.2.  Bug #1 is filed for this issue.
> As the maintainer of the script, I test a few things between bash-4.2
> and bash-5.1 and I come up with this workaround:
>
> unicorn:~$ cat foo
> #!/bin/bash
> template='The best candy is clearly @CANDY@!'
> candy='M&Ms'
> printf '%s\n' "${template/@CANDY@/$candy}"    # unquote $candy to fix bug
> #1
>
> unicorn:~$ bash-4.2 ./foo
> The best candy is clearly M&Ms!
> unicorn:~$ bash-5.1 ./foo
> The best candy is clearly M&Ms!
>
> Now it works on older systems too.  Everything's fine... until bash-5.2.
>
> unicorn:~$ bash-5.2 ./foo
> The best candy is clearly M@CANDY@Ms!
>
> The workaround for bug #1 causes bug #2 on bash-5.2.  To make the script
> work on all three versions of bash, we need a different workaround:
>
> unicorn:~$ cat foo
> #!/bin/bash
> template='The best candy is clearly @CANDY@!'
> candy='M&Ms'
> message=${template/@CANDY@/"$candy"}          # Work around bug #1 and #2.
> printf '%s\n' "$message"
>
> unicorn:~$ bash-4.2 ./foo
> The best candy is clearly M&Ms!
> unicorn:~$ bash-5.1 ./foo
> The best candy is clearly M&Ms!
> unicorn:~$ bash-5.2 ./foo
> The best candy is clearly M&Ms!
>
> And there you have it.  You're allowed to quote "$candy" in a variable
> assignment, as long as the whole parameter expansion ${...} remains
> unquoted, and it'll work properly in all 3 versions.  I'm using "message"
> as a temporary variable, whose sole purpose is to work around this issue.
>

mate , thank you for investing time in explainmennts

what on yours i ask , o i see now , 4.2 ..
i quote right in ${ // - to me , preserved quotes are • an invalid youth
bug to be replaced with better by bash.c changes
which it seemfully did

is quotes preserveness the only bug here i see ?

root@localhost:~# a=i_am_foo b=_ c=${b}am$b d=${b}be$b e=${a//"$c"/"$d"} ;
printf ' -->  %s\n' "$e" "${a//"$c"/"$d"}"
 -->  i_be_foo
 -->  i_be_foo

for me , trying to support such wrongness , resulted ( along other same
logics.. ) in a 'best is newest upstream version' rule

>