cell sublanguage: unset -v 'a[0]' (ble.sh)

[akinomyoga]

I use this construct in ble.sh. I could find some test case for this here and also some mentions on unset a[0] here, but it doesn't work with the current Oil. Is this a regression?

$ bin/osh -c 'a=(x y z); unset "a[1]"'
  a=(x y z); unset "a[1]"
                   ^
[ -c flag ]:1: 'unset' got invalid variable name 'a[1]'
[ble: exit 2]
$ bin/osh -c "a=(x y z); unset 'a[1]'"
  a=(x y z); unset 'a[1]'
                   ^
[ -c flag ]:1: 'unset' got invalid variable name 'a[1]'
$

[andychu]

OK we may need to do dynamic parsing of a[const] within several constructs:

• unset
• ${!ref}
• declare -n (nameref)

And maybe a few other places... @abathur also used this with -n.

It will parse a[const] but not a[1+2] since the latter would parse arbitrary code.

Somewhere on the blog I called this the "cell sublanguage", oh yeah here: http://www.oilshell.org/blog/2019/02/07.html#appendix-a-minor-sublanguages

[andychu]

#608 is the feature for nameref

[andychu]

note: marked with two stars on #653

[andychu]

May relate to IR in #604 , e.g. sh_lhs_expr

[andychu]

@akinomyoga Another thing I wanted to ask is if you're using only indexed arrays for

unset -v a[0]

Or if you're also using associative arrays? The latter is trickier

$ declare -A A=(['foo']=bar)
$ echo ${A[@]}
bar
$ unset -v "A['foo']"
-bash: unset: A['foo']: bad array subscript

$ unset -v "A[foo]"
$ echo ${A[@]}
(empty)

It doesn't like the quotes, and prefers bare word syntax, which is inconsistent with the rest of Oil (and bash to some extent)

[akinomyoga]

Thank you.

Another thing I wanted to ask is if you're using only indexed arrays

Yes, I searched in ble.sh source and it seems unset is currently only used for indexed arrays. But that's not intentional and I'm not sure if I will never use it forever. And, it is a little bit awkward that there is no means to remove a key from associative arrays.

It doesn't like the quotes,

Which version of Bash do you use? I tried with versions of Bash and found that the behavior was changed since 4.4. I think it was a bug of Bash.

$ bash --norc # bash-4.4 or 5.0
$ declare -A A=(['foo']=bar)
$ declare -p A
declare -A A=([foo]="bar" )
$ unset -v "A['foo']"
$ declare -p A
declare -A A=()

The safe way for unsetting an associative array element in Bash that should work with an arbitrary key is the following. I think Oil can support this form.

$ declare -A d
$ key="a]b'c[d"   # A key containing special characters
$ unset -v 'd[$key]'

[andychu]

OK yes, I was testing on my machine which is bash 4.3. I did it through the spec tests and bash behaves consistently with associatve arrays for unset -v, declare -n, and ${!ref} ( see the last 3 test cases in commit above).

So I think we can probably do it, though I might start with just a[0] and see what we can get to run first.

[andychu]

OK this can be tested from master... Looking at #640 now (which is different than #648 in Oil)