bug#52873: expr unexpected syntax error
ok I appreciate the explanation.
On Wed, 29 Dec 2021 at 20:58, Paul Eggert wrote:
> On 12/29/21 12:01, Martin Rixham wrote:
> > What nonsense. I want to parse source code. ')' is not an uncommon line
> of
> > source code. It should work.
>
> Unfortunately, you're asking for what is in general impossible. If the
> left argument of ':' could be any string, then the grammar for 'expr'
> would be ambiguous. Consider the following shell command:
>
> expr '(' : ')'
>
> This outputs ':' because it evaluates the parenthesized string ':'; but
> if the operands of ':' could be any strings it could also be interpreted
> as matching '(' against ')', which means it should output the same thing
> as 'expr a : b', namely '0'.
>
> Of course this means 'expr' was poorly designed in the 1970s, but we're
> stuck with that design now (it's standardized by POSIX), portable code
> must deal with this poor design, and for compatibility reasons it's
> better for GNU expr to support the design, poor as it is.
>
> These days there are much better ways than 'expr' to parse code. For
> example, if you want to count the number of characters in a shell
> variable v, you can use this shell command:
>
> nv=${#v}
>
> This works even if v=')', whereas this:
>
> nv=$(expr "$v" : '.*')
>
> has the bug that you mentioned, plus it's harder to read and it's less
> efficient.
>
bug#52873: expr unexpected syntax error
What nonsense. I want to parse source code. ')' is not an uncommon line of
source code. It should work.
On Wed, 29 Dec 2021 at 19:52, Paul Eggert wrote:
> On 12/29/21 08:31, Davide Brini wrote:
> > I think you need to use '+' before the offending token
>
> Yes. That's a GNU extension. If you want to be portable to any POSIX
> implementation, you can use this instead:
>
> expr "X(" : '.*' - 1
>
> A similar example is given in the POSIX spec for 'expr':
>
> https://pubs.opengroup.org/onlinepubs/9699919799/utilities/expr.html
>
> As this is not a bug, I'm closing the bug report.
>
bug#52873: expr unexpected syntax error
I'm getting an error from the following:
[martin@fedora ~]$ expr ')' : '.*'
expr: syntax error: unexpected ')'
There also seems to be a similar problem with:
expr '(' : '.*'
Here's the version:
[martin@fedora ~]$ expr --version
expr (GNU coreutils) 8.32
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <
https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by Mike Parker, James Youngman, and Paul Eggert.
And a uname for good measure:
[martin@fedora ~]$ uname -a
Linux fedora 5.15.7-200.fc35.x86_64 #1 SMP Wed Dec 8 19:00:47 UTC 2021
x86_64 x86_64 x86_64 GNU/Linux
Thanks,
Martin
