On Mon, 23 Jun 2025 at 19:02, Takaaki Konno <[email protected]> wrote:
>
> x=abc
> case def in
> "${x#abc}"def) ;;
> "${x##abc}"def) ;;
> "${x%abc}"def) ;;
> "${x%%abc}"def) ;;
> "${x/abc/}"def) ;;
> "${x//abc/}"def) ;;
> "${x/#abc/}"def) ;;
> "${x/%abc/}"def) ;;
> *) echo 'not matched'
> esac
> # => not matched
>
Curiously, variations of this issue have existed for a VERY long time,
since bash-3.00.0(92)-release (commit
b80f6443b6b7b620c7272664c66ecb0b120a0998). At that stage only these forms
were affected:
x=def
case abc in
> "${x::0}"abc) ;;
> "${x:1:0}"abc) ;;
> *) echo FAILED ;;
> esac
>
This got worse in 3.00.16(91)-release (commit
eb87367179effbe5f430236db8259006d71438b7) where these also failed:
x=def
case abc in
> "${x:3}"abc) ;;
> *) echo FAILED ;;
> esac
In bash-3.1-rc2 (commit 28089d04354f1834f109bcb4730c9200234861bc) it just
got weird: when quoted "${x:3}" started expanding to a DEL (\x7f) byte (but
the ${x:1:0} expansion did not, though the case match still failed).
This was also present in the master branch at bash-3.2.0(85)-beta (commit
e7f1978acfd2125b69bca36994882a1333607739).
It seemed to be fixed in bash-3.2.0(83)-release (commit
0628567a28f3510f506ae46cb9b24b73a6d2dc5d)
But then it gets worse, in bash-4.0.0p1-alpha (commit
f2f9854dfd1a35d3b2b10d5b59b96e951a45c3fe), where in addition all
pattern-matching expansions are broken (but without resulting in apparent
DEL bytes).
x=def
> case abc in
> "${x#def}"abc) ;;
> "${x%def}"abc) ;;
> "${x/def}"abc) ;;
> "${x/#def}"abc) ;;
> "${x/%def}"abc) ;;
> *) echo FAILED ;;
> esac
Since then the mismatch problem seems to have remained unchanged.
The problem does not occur if there is anything else inside the quotes with
the expansion, like
x=def
> case abc in
> "${x#def}abc") echo SUCCESS ;;
> esac
or if the expansion is unquoted (as noted by Konno-san), like
x=def
> case abc in
> ${x#def}abc) echo SUCCESS ;;
> esac
-Martin
PS: I suspect the DEL bytes are somehow still present when expanding a
variable with a modifier within a case pattern, but not when the same thing
is expanded elsewhere.
