Re: why fail , [[ $sep$*$sep == $sep--$sep ]]

[Lawrence Velázquez]

On Sun, Feb 18, 2024, at 8:51 AM, Kerin Millar wrote:
> On Sun, 18 Feb 2024 14:34:43 +0100
> alex xmb sw ratchev <fxmbsw7@gmail.com> wrote:
>
>> On Sun, Feb 18, 2024, 14:18 Kerin Millar <kfm@plushkava.net> wrote:
>> 
>> > On Sat, 17 Feb 2024 17:01:13 +0100
>> > alex xmb sw ratchev <fxmbsw7@gmail.com> wrote:
>> >
>> > > oh i know why it failed
>> > > set interprets the first -- away
>> >
>> > That is not why it is failing to behave as you expect. Rather, the issue
>> > is that your conditional expression is incorrect. It should be [[ "$f$*$f"
>> > == *"$f--$f"* ]]. Note that you have chosen to change the value of IFS. It
>> > is important that you do not omit the quotes - not even for the left hand
>> > side of the expression!
>> >
>> 
>> i thought there is a ' flat left side of == '
>
> Unfortunately, the raw output of xtrace is not much use for human 
> eyeballs. Here's the exact difference.
>
> $ ( set aa bb cc -- dd; f=$'\1' IFS=$f PS4= BASH_XTRACEFD=1; set -x; [[ 
> "$f$*$f" == *"$f--$f"* ]] ) | hexdump -C
> 00000000  5b 5b 20 01 61 61 01 62  62 01 63 63 01 2d 2d 01  |[[ 
> .aa.bb.cc.--.|
> 00000010  64 64 01 20 3d 3d 20 2a  01 5c 2d 5c 2d 01 2a 20  |dd. == 
> *.\-\-.* |
> 00000020  5d 5d 0a                                          |]].|
>
> $ ( set aa bb cc -- dd; f=$'\1' IFS=$f PS4= BASH_XTRACEFD=1; set -x; [[ 
> $f$*$f == *"$f--$f"* ]] ) | hexdump -C
> 00000000  5b 5b 20 61 61 62 62 63  63 2d 2d 64 64 20 3d 3d  |[[ 
> aabbcc--dd ==|
> 00000010  20 2a 01 5c 2d 5c 2d 01  2a 20 5d 5d 0a           | *.\-\-.* 
> ]].|

This surprises me because IFS is not lost if it's set to something
a little less ... weird:

$ (set aa bb cc -- dd; f=+ IFS=$f; set -x; [[ $f$*$f == *"$f--$f"* ]])
+ [[ +aa+bb+cc+--+dd+ == *\+\-\-\+* ]]

Why the difference?

-- 
vq