Re: Different variable assignments

Liste des GroupesRevenir à cu shell 
Sujet : Re: Different variable assignments
De : Lem (at) *nospam* none.invalid (Lem Novantotto)
Groupes : comp.unix.shell
Date : 13. Oct 2024, 00:07:41
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <veevft$aqpc$1@dont-email.me>
References : 1 2 3 4 5 6 7 8
User-Agent : Pan/0.160 (Toresk; )
Il Sat, 12 Oct 2024 17:57:16 +0200, Frank Winkler ha scritto:

I'm still thinking about the difference between "< <(...)" and "<<<`...`"

As already pointed out by Lawrence:

1) "command2 <<<`command1`": `command2`, equal to the preferable[*]
$(command2), can be seen as the output of command2: a string. So with
<<< you are telling the shell to take this string as input on the
standard input of command2. So: execute command1, then take its output
as the input of command2. This is called *command* substitution:
substitution of a command with its output.

[*] No characters are special between parenthesis: easier.

2) "command2 < <(process_of_command1)": here process, which is the
"active running instance" of command1 - enough: remove the difference,
think of command1 and stop - is run with its output connected to a
named FIFO pipe file (or to some file in /dev/fd).
So <(process_of_command1) is expanded as the name of this file.
The first < is simple input redirection.
So: execute command1, connect the output of its process to a special
file, redirect this special file to input of command2.
This is called *process* output substitution: substitute a
process with the name of its output file.
Process substitution does work only on systems supporting named pipes
or /dev/fd/... so it's less universal than command substitution.

Some practical differences. For example, try:

$ cat <<<$(while true; do echo yes; done)

Nothing: cat is waiting for the other stuff to end. But it won't end,
in this case! Gawsh!

$ cat < <( while true; do echo yes; done)

Rock'n'roll!

And I would be happy with this one if there was a notation "the other
way round"  ... something like "... >>> $var"

You're more the straightforward type of guy, eh! That's fine! ;)
But, sorry, '>>>' is still to come. In bash, at least. :-)
--
Bye, Lem

Date Sujet#  Auteur
11 Oct 24 * Different variable assignments60Frank Winkler
11 Oct 24 +* Re: Different variable assignments33John-Paul Stewart
11 Oct 24 i`* Re: Different variable assignments32Frank Winkler
12 Oct 24 i `* Re: Different variable assignments31Janis Papanagnou
12 Oct 24 i  +* Re: Different variable assignments5Lawrence D'Oliveiro
19 Oct 24 i  i`* Re: Different variable assignments4Kenny McCormack
19 Oct 24 i  i `* Re: Different variable assignments3Janis Papanagnou
19 Oct 24 i  i  `* coprocs in bash & ksh (Was: Different variable assignments)2Kenny McCormack
19 Oct 24 i  i   `- Re: coprocs in bash & ksh (Was: Different variable assignments)1Janis Papanagnou
12 Oct 24 i  +* Re: Different variable assignments24Frank Winkler
12 Oct 24 i  i+- Re: Different variable assignments1Lawrence D'Oliveiro
12 Oct 24 i  i`* Re: Different variable assignments22Janis Papanagnou
12 Oct 24 i  i +* Re: Different variable assignments20Lem Novantotto
12 Oct 24 i  i i`* Re: Different variable assignments19Frank Winkler
12 Oct 24 i  i i +* Re: Different variable assignments3Lem Novantotto
19 Oct 24 i  i i i`* lastpipe (Was: Different variable assignments)2Kenny McCormack
19 Oct 24 i  i i i `- Re: lastpipe (Was: Different variable assignments)1Lem Novantotto
12 Oct 24 i  i i +* Re: Different variable assignments4Lawrence D'Oliveiro
12 Oct 24 i  i i i`* Re: Different variable assignments3Janis Papanagnou
12 Oct 24 i  i i i `* Re: Different variable assignments2Lawrence D'Oliveiro
12 Oct 24 i  i i i  `- Re: Different variable assignments1Janis Papanagnou
13 Oct 24 i  i i +* Re: Different variable assignments3Lem Novantotto
13 Oct 24 i  i i i+- Re: Different variable assignments1Lem Novantotto
13 Oct 24 i  i i i`- Re: Different variable assignments1Lem Novantotto
15 Oct 24 i  i i `* Re: Different variable assignments8Frank Winkler
24 Oct 24 i  i i  `* Re: Different variable assignments7Frank Winkler
24 Oct 24 i  i i   +* Re: Different variable assignments3Kenny McCormack
24 Oct 24 i  i i   i`* Re: Different variable assignments2Frank Winkler
25 Oct 24 i  i i   i `- Re: Different variable assignments1Janis Papanagnou
25 Oct 24 i  i i   `* Re: Different variable assignments3Lem Novantotto
25 Oct 24 i  i i    `* tee with no args is a no-op (Was: Different variable assignments)2Kenny McCormack
25 Oct 24 i  i i     `- Re: tee with no args is a no-op (Was: Different variable assignments)1Lem Novantotto
12 Oct 24 i  i `- Re: Different variable assignments1Frank Winkler
19 Oct 24 i  `- lastpipe (Was: Different variable assignments)1Kenny McCormack
11 Oct 24 `* Re: Different variable assignments26Helmut Waitzmann
11 Oct 24  +* Re: Different variable assignments23Frank Winkler
11 Oct 24  i+* Re: Different variable assignments21Lawrence D'Oliveiro
19 Oct 24  ii`* Re: Different variable assignments20Kenny McCormack
19 Oct 24  ii `* Re: Different variable assignments19Janis Papanagnou
19 Oct 24  ii  +* coproc or whatever in bash and ksh (Was: Different variable assignments)4Kenny McCormack
19 Oct 24  ii  i`* Re: coproc or whatever in bash and ksh (Was: Different variable assignments)3Janis Papanagnou
19 Oct 24  ii  i +- Re: coproc or whatever in bash and ksh (Was: Different variable assignments)1Janis Papanagnou
19 Oct 24  ii  i `- Re: coproc or whatever in bash and ksh (Was: Different variable assignments)1Kenny McCormack
19 Oct 24  ii  `* Re: Different variable assignments14Lawrence D'Oliveiro
20 Oct 24  ii   `* Re: Different variable assignments13Kenny McCormack
20 Oct 24  ii    `* Re: Different variable assignments12Janis Papanagnou
20 Oct 24  ii     `* coprocs - again (Was: Different variable assignments)11Kenny McCormack
25 Oct 24  ii      `* Re: coprocs - again (Was: Different variable assignments)10Janis Papanagnou
25 Oct 24  ii       +* Re: coprocs - again (Was: Different variable assignments)8Lawrence D'Oliveiro
25 Oct 24  ii       i+* Re: coprocs - again (Was: Different variable assignments)6Janis Papanagnou
25 Oct 24  ii       ii`* Subjective "valuations" are all we have (Was: coprocs - again (Was: Different variable assignments))5Kenny McCormack
25 Oct 24  ii       ii `* Re: Subjective "valuations" are all we have (Was: coprocs - again (Was: Different variable assignments))4Janis Papanagnou
25 Oct 24  ii       ii  +- Re: Subjective "valuations" are all we have (Was: coprocs - again (Was: Different variable assignments))1Lem Novantotto
25 Oct 24  ii       ii  `* Re: Subjective "valuations" are all we have (Was: coprocs - again (Was: Different variable assignments))2Kenny McCormack
26 Oct 24  ii       ii   `- Re: Subjective "valuations" are all we have (Was: coprocs - again (Was: Different variable assignments))1Janis Papanagnou
25 Oct 24  ii       i`- Re: coprocs - again (Was: Different variable assignments)1Kenny McCormack
25 Oct 24  ii       `- How to do multiple concurrent coprocs in ksh (Was: coprocs - again (Was: Different variable assignments))1Kenny McCormack
12 Oct 24  i`- Re: Different variable assignments1Christian Weisgerber
15 Nov 24  `* Re: Different variable assignments2Kenny McCormack
16 Nov 24   `- Re: Different variable assignments1Lem Novantotto

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