Trying to figure out when spaces are and aren't allowed in ${blah} led to asking
why echo ${!a* } is an error but ${!a@ } isn't (when there are no variables
starting with a), and I eventually worked out that:
$ X=PWD
$ echo ${!X@Q}
'/home/landley/toybox/clean'
Is going on? Which is just weird, both because:
$ echo ${PATH@ }
bash: ${PATH@ }: bad substitution
And because:
$ ABC=defghi; echo ${#ABC@Q}
bash: ${#ABC@Q}: bad substitution
$ echo ${PWD:1:3@Q}
bash: PWD: 3@Q: value too great for base (error token is "3@Q")
$ echo ${PWD:1@Q}
bash: PWD: 1@Q: value too great for base (error token is "1@Q")
Hmmm...
$ echo ${!potato@walrus}
$ echo ${!P@walrus}
$ echo ${!P@}
PATH PIPESTATUS PPID PS1 PS2 PS4 PWD
$ X=PATH
$ echo ${!X@ }
bash: ${!X@ }: bad substitution
$ ABC=123
$ echo ${!A@walrus}
$ echo ${!ABC@}
ABC
$ echo ${!ABC@walrus}
$ echo ${!A@ }
Ok, when X exists and points to another variable, then !X becomes the contents
of that other variable and THEN the @ cares about trailing garbage. But * is a
different codepath from @...?
And when the ${!var} doesn't have contents pointing to another existing
variable, it falls back to a codepath that tries the prefix stuff (and/or the
array stuff, in some order?) and that codepath tries to parse trailing @Q and
friends, but DOESN'T error out if it can't recognize the trailing stuff after
the @?
I'm pretty sure the array mangling logic ties in here somehow, but there's some
missing error checking somewhere...
Anyway, I'm confused again. Did I miss something in the man page?
$ ABC=PATH
$ echo ${!ABC:1:2@Q}
bash: !ABC: 2@Q: value too great for base (error token is "2@Q")
$ echo ${!ABC:1:2 @Q}
bash: !ABC: 2 @Q: syntax error: invalid arithmetic operator (error token is
"@Q")
Which to be honest is more like what I expected, it sees the : and goes "ah,
consume the remainder in THIS mode"...
$ echo ${abc#23@Q}
123
But if ANYTHING was going to recognize @Q at the end of another operation I'd
expect it to be : which already has to recognize further punctuation, but no:
$ ABC=123; echo ${ABC:@Q}
bash: ABC: @Q: syntax error: operand expected (error token is "@Q")
Rob
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