Bug 496791

Michal, thanks for your report.

I'm not sure, whether this is really a bug report, thus I'm Cc'ing upstream of
mksh. Thorsten will be able to clarify this.

(In reply to comment #1)
> Michal, thanks for your report.
> 
> I'm not sure, whether this is really a bug report, thus I'm Cc'ing upstream of
> mksh. Thorsten will be able to clarify this.  

Why this should not be bug? Mksh produces error for syntactically correct script.

FYI:
bash and ksh works
zsh was recently fixed (see bug #484348)

I think this counts as bug. Thanks for reporting.
Note that this problem was inherited from pdksh.

I will try to fix it upstream when I have got the time.

Thorsten, thank you for answering. Michal, I didn't know, whether $() really
has to work or whether it's a bash/ksh/zsh only thing. Fix will be reflected
to all active Fedora/EPEL branches with the next mksh release or similar.

Commit ID:      10049EF448F5F89A278
CVSROOT:        /cvs
Module name:    (multiple)
Changes by:     tg.org      2009/04/22 16:25:15 UTC

Modified files:
        bin/mksh       : mksh.1
        src            : mksh.hts

Log message:
address RedHat BZ#496791: fix currently not possible, because the code
which escapes $(…) content does not know if an imbedded ‘#’ is a comment
leader or something else like “16#foo”, “${#bla[*]}”, “${foo#bar}”, &c.
and the comment skip code does not know about nesting beforehand
⇒ document this problem in the place where it already documents that
  the current code does not properly handle nested $($(…)) expressions

patches welcome

To generate a diff of this changeset, execute the following commands:
cvs -R rdiff -kk -upr1.157 -r1.158 src/bin/mksh/mksh.1
cvs -R rdiff -kk -upr1.226 -r1.227 www/src/mksh.hts

This means: I cannot fix this bug, while I agree it being one.

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I’ve got a workaround:

tg@blau:~ $ cat x
#!/bin/mksh
# Comment containing '
VAR=$(eval $(cat)) <<"EOF"
echo a
# Comment containing '
EOF
echo $VAR
tg@blau:~ $ mksh x
a

Same thing is now documented in the manual page, BUGS section:

     Some parts of the parser are not recursive; things like the following ex-
     ample will fail because of the parenthesis asymmetry (RedHat BZ#496791).
     A workaround exists; use 'x=$(cat) <<"EOF"' instead if you merely want to
     slurp the string.

           x=$(case $foo in bar) echo $bar ;; *) echo $baz ;; esac)
           # above fails; below is the workaround
           x=$(eval $(cat)) <<"EOF"
           case $foo in bar) echo $bar ;; *) echo $baz ;; esac
           EOF

This may not be a proper/real fix, but unless there will be a
rewrite of a lot of internals (not just the parser; these things
appear to be even more intertwined with each other than I originally
thought) this is the best I can do…

I’ve just committed code that fixes this bug, in the most detailed
way possible by parsing command substitutions recursively, then
inserting a tree dump into place.

This is still considered EXPERIMENTAL code, though, and as such
should not be backported or used in production systems (yet).

As I suspected, this change (which rewrote a third of the lexer and some of the parser) needs quite some others, including fixes to the tree code (some decades old pdksh heritage) and rewrites of another half or so of the lexer to work well. I’m still trying to squash all the bugs in mksh-current, FWIW. But we have extensive testcases now, so backporting can, while difficult, be validated afterwards.

This has been solved for quite a while now.