Re: Quoting and string comparison

[Ilkka Virta]

On 8.2. 15:05, Jaan Vajakas wrote:
> Hi!
>
> I noticed a weird behavior. Is it a bug?
>
> Namely, why does
>
> echo "$(for f in a b c; do if [[ \"$f\" > b ]]; then echo "$f > b"; else
> echo "$f <= b"; fi; done)"

If I'm not mistaken, what you're doing is essentially this:

$ for f in '"a"' '"b"' '"c"'; do if [[ $f > b ]]; then echo "$f > b"; 
else echo "$f <= b"; fi; done

i.e., since you added the escaped quotes, you're testing strings with 
quotes against a string without one. The result is very likely to depend 
on your locale.

With LC_COLLATE="en_US.UTF-8", I get:

"a" <= b
"b" > b
"c" > b

Here, the first quote is effectively ignored unless it's the only 
difference.


With LC_COLLATE=C, I get

"a" <= b
"b" <= b
"c" <= b

Here, the comparison stops when the first quote is compared against the 
letter b.


I'm not sure what the command substitution is supposed to do here, apart 
from confusing the command. The quotes inside the command substitution 
are independent of the quotes outside of it. I'm not sure if you already 
know this or not, since you only escaped _some_ of them.

> I would have expected the same output as one of
> echo "$(for f in a b c; do if [[ "$f" > b ]]; then echo "$f > b"; else echo
> "$f <= b"; fi; done)"

Here, there are no quotes in the string to be compared, you've just 
quoted the string on the left-hand side. The quotes are removed as usual 
before the string is compared.

> echo "$(for f in a b c; do if [[ '"$f"' > b ]]; then echo "$f > b"; else
> echo "$f <= b"; fi; done)"

Here, the left-hand side is single-quoted, so the variable is not 
expanded, and the comparison is of a fixed string against another.

> This happens e.g. on GNU Bash v4.4 (e.g.
> https://www.tutorialspoint.com/execute_bash_online.php ).
>
>
> Best regards,
> Jaan


--
Ilkka Virta / itvirta@iki.fi