dash bug with string expansion and assignment of default values (#1757) · Issues · Development / openfoam

dash bug with string expansion and assignment of default values

Noticed when compiling OpenFOAM-v2006 modules with ubuntu bionic (18.04) that the module prefix is not being correctly set. Seems to be a weird bug in the dash shell expansions.

Starting from any non-root directory

echo "$PWD"
-> /home/user/openfoam/BuildEnv/scratch

dash 0.5.8-2.10 (bionic) shows this

unset test1
echo "${test1:=${PWD%/*}}"
-> /home/user/openfoam/BuildEnv/scratch  <-- WHAT?? Not what we expected

The additional quotes cause incorrect expansion. Whereas

unset test1
echo ${test1:=${PWD%/*}}
-> /home/user/openfoam/BuildEnv  <-- Expected

bash and dash 0.5.10.2-6 (focal) work as expected, with/without quotes
quoted expansion with :- works as expected.

Possible fixes?

Possible workarounds

use unqoted version, but risk fixing it on the next shellcheck
explicit if [ -z VAR ]; then ...; fi construct
with dirname as : "${VAR:=$(dirname xxx)}

Noticed when compiling OpenFOAM-v2006 modules with ubuntu _bionic_ (18.04) that the module prefix is not being correctly set. Seems to be a weird bug in the `dash` shell expansions.

Starting from any non-root directory
```
echo "$PWD"
-> /home/user/openfoam/BuildEnv/scratch
```
dash 0.5.8-2.10 (bionic) shows this
```
unset test1
echo "${test1:=${PWD%/*}}"
-> /home/user/openfoam/BuildEnv/scratch  <-- WHAT?? Not what we expected
```
The additional quotes cause incorrect expansion. Whereas
```
unset test1
echo ${test1:=${PWD%/*}}
-> /home/user/openfoam/BuildEnv  <-- Expected
```

- bash and dash 0.5.10.2-6 (focal) work as expected, with/without quotes
- quoted expansion with `:-` works as expected.

Possible fixes?
- https://git.kernel.org/pub/scm/utils/dash/dash.git/commit/?id=48ca00863af909461d1372998bb90549f27abaaf
- https://git.kernel.org/pub/scm/utils/dash/dash.git/commit/?id=a29e9a1738a4e7040211842f3f3d90e172fa58ce
- https://git.kernel.org/pub/scm/utils/dash/dash.git/commit/?id=878514712c5d21f675c45d99d2f8a04098ea4a19

Possible workarounds
- use unqoted version, but risk fixing it on the next shellcheck
- explicit `if [ -z VAR ]; then ...; fi` construct
- with dirname as `: "${VAR:=$(dirname xxx)}`

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