Re: how does bash parse back-ticks, anyway?

[Sven Mascheck]

Eric Blake wrote:

> Read the POSIX rationale:
> http://www.opengroup.org/onlinepubs/009695399/xrat/xcu_chap02.html

> | [...] While the newer "$()" form can process
> | any kind of valid embedded script, the backquoted form cannot handle
> | some valid scripts that include backquotes. For example, these
> otherwise
> | valid embedded scripts do not work in the left column, but do work
> on
> | the right:
> |
> |     echo `                         echo $(
> |     cat <<\eof                     cat <<\eof
> |     a here-doc with `              a here-doc with )
> |     eof                            eof
> |     `                              )
> |
> |     echo `                         echo $(
> |     echo abc # a comment with `    echo abc # a comment with )
> |     `                              )

BTW,

My bash-3.2.15(1)/libc2.3.6/i686-pc-linux-gnu-2.6.13 (like previous
releases) fails on the first $() example.  It also fails if the
here-doc contains a single, double or back quote instead of the ).

"case x in x)" in $() is also not accepted; this is to be worked
around with "case x in (x)" (POSIX is stricter, though).

Academic failure: an embedded here-doc, with unproblematic content,
but ) as delimiter instead of eof.


[ksh93 and all almquist shells are robust about all these.
 zsh and pdksh behave very similar to bash.]

[[The second $() example from above was fixed with bash-3.2]]