RFC/E: more simplification / dropping of unnecessary quotes

[scop]

It seems there's room for some more removal of unnecessary quotes on simplify; to my knowledge word splitting does not occur:

• within [[ ]] -- some quotes are removed in this context already, but not e.g from the right side of things like [[ $foo == "$bar" ]]
• on assignment (= and +=)

I don't know offhand how this is for other shells besides bash, but thought I'd drop the suggestion here for comments already based just on the bash info.

[akinomyoga]

Similarly, in Bash, case $word in and here strings <<< $word are unnecessary in most cases. Some notes:

• The quotes in the right-hand sides of ==, !=, and =~ in conditional commands [[ ]] should not be removed. The quote has special meaning in those contexts.
• When a word on the right-hand side of assignments and [[ ... ]] contains $* or ${arr[*]}, they need to be quoted as "$*" or "${arr[*]}". Bash <= 4.2 has a bug that the joining character (the first character of IFS) is replaced by a whitespace .
• Similarly, when a word in case and in here documents contain $* or ${arr[*]}, they need to be quoted. Bash <= 4.4 has a bug.

• Needless to say, when the word contains literal shell special characters [[:space:]|&;<>\`"$], the quote for these characters cannot be removed. For example, var="a b c" cannot be unquoted to be var=a b c.

  Edit: Bash <= 4.3 has a bug in here strings: https://github.com/koalaman/shellcheck/issues/1009#issuecomment-488395630, so here strings need to be quoted as far as bash <= 4.3 is supported.

[scop]

Thanks for the info. What I'm specifically thinking of are the simple "$foo" cases. Any known issues dropping the quotes from them in the mentioned contexts?

[akinomyoga]

For the simple case "$foo", I think there aren't any problems in the mentioned contexts at least in Bash. They can be always unquoted in

• the right-hand sides of assignments (var=$foo),
• the conditional commands (except for the right-hand sides of ==, !=, and =~) ([[ $foo == "$bar" ]]),
• the target of the case statements (case $foo)
• and the here documents (<<< $foo) edit: Bash <= 4.3 has a bug in here strings: https://github.com/koalaman/shellcheck/issues/1009#issuecomment-488395630, so here strings need to be quoted as far as bash <= 4.3 is supported.