Re: Question on $IFS related differences (Was: Question on $@ vs $@$@)

[Steffen Nurpmeso]

Hello Robert.

Thanks again for your extensive answers.

Robert Elz wrote in
 <2675.1726728154@jacaranda.noi.kre.to>:
 |    Date:        Thu, 19 Sep 2024 00:45:44 +0200
 |    From:        Steffen Nurpmeso <steffen@sdaoden.eu>
 |    Message-ID:  <20240918224544.aXWgbZu-@steffen%sdaoden.eu>
 |
 || Woops.  I did not know that, i always separate {} at the beginning
 || an the end, yet not ().
 |
 |'(' and ')' (parentheses) are operators, '{' and '}' (braces) are not,

(And metacharacters that "separate words".  I say that because,
yes, the MUA knows that concept .. but excludes &()<> for several
reasons.)

 |nor are '[' and ']' (brackets) - though I have never really understood
 |bash's rules for '[[' and ']]' in this context.
 |
 |Also note that things tend to change meaning if immediately after
 |an unquoted '$' (or an unsecaped double quoted "$").
 |
 ||   #?255|kent:steffen$ dash -c '{echo du;}'
 ||   dash: 1: Syntax error: "}" unexpected
 |
 |That's because to get the reserved word '{' you first need to
 |get the word '{' and you don't there, the first word is '{echo'
 |which is just another command name, probably unlikely to exist.
 |
 |Hence when the '}' is seen, which is a separate word, as it
 |follows an operator (';') and being in the command word position
 |is recognised as the reserved word '}' you now have a syntax
 |error from the grammar, as a '}' reserved word is only allowed
 |after an opening '{' reserved word, which does not exist here.

Good to know.  I wondered how deep this knowledge is into the
shell programming/hacking community, i think i have--consciously--
never seen this before.  From looking at available things,
nothing.

 |Take a slightly different example
 |
 | $SHELL -c '{echo du>}'
 |
 |That would "work" (if you had a '{echo' command -- binary, script, or
 |function) as '>' is an operator, so there are 3 words and an operator
 |there:
 | '{echo' 'du' > '}'
 |where I put quotes (which change nothing, as there are no reserved words
 |here, the only candidate would be '{echo') around the words, but not the
 |operator (as if there were quotes it would not be an operator).
 |
 |Syntactically that's no different than
 |
 | 'echo' 'foo' > 'file'

I see.

 ||   #?2|kent:steffen$ dash -c '{ echo du;}'
 ||   du
 |
 |There '{' is a word by itself (white space delimited) in the command
 |word position, and so becomes the reserved word '{' (it wouldn't if
 |actually quoted of course, but would still be a separate word because
 |of the following, unquoted, white space).   Then the rest of the syntax
 |is all fine (the same as the first example) and it all works.
 |
 ||   #?0|kent:steffen$ bash -c '{echo du;}'
 |
 |There's no real need to test this kind of thing with different shells,
 |all this is very well understood, and should be the same everywhere
 |(at least provided that none of the disgusting evil that is aliases
 |gets involved.)

We remember your often iterated stance.

 |While I am here, a hint for script writers - always put white space
 |(of some form) around operators (unlike the examples above).  It isn't
 |required by the syntax, but recognising operators always takes the
 |longest sequence of characters that represent any valid operator,
 |and while a sequence (like the '>}' I used above) might not be a valid
 |operator today, who knows what might happen tomorrow?   There are
 |however some combinations (like the ';}') that are so commonly used
 |that no shell author is going to break the world by usurping those,
 |another is '>&-' (and similar for other redirect operators) where
 |the '>&' is an operator, but '-' is just the following word, and
 |'>& -' means just the same -- except for '<<-' which is an operator,
 |and quite different from '<< -'.
 |
 |kre
 --End of <2675.1726728154@jacaranda.noi.kre.to>

Ciao, and greetings from Germany,

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)