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From: Janis Papanagnou <janis_papanagnou+ng@hotmail.com>
Newsgroups: comp.unix.shell
Subject: Re: Different variable assignments
Date: Sat, 12 Oct 2024 23:47:34 +0200
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On 12.10.2024 23:32, Lawrence D'Oliveiro wrote:
> On Sat, 12 Oct 2024 17:57:16 +0200, Frank Winkler wrote:
> 
>> I'm still thinking about the difference between "< <(...)" and "<<<
>> `...`"
> 
> Not sure about the extra “<”,

'<(...)' executes the command indicated by '...' and provides a file
descriptor, something like '/dev/fd/5', which (being effectively a
filename) can be redirected to the 'read' command.

The shell's 'read' command doesn't read from files but from stdin,
so if 'read's input is in a file or is the output of a command (as in
this case) you have to do a redirection; for the first case
  read < file
and in case of a process substitution (a file named like /dev/fd/5)
  read < <(some command)
which sort of "expands" to something like
  read < /dev/fd/5

So it's no "extra" '<', it's just a necessary redirection for a
command that reads from 'stdin' but not from files.

Janis

> but “<(«cmd»)” gets substituted with the 
> name of a file (i.e. not stdin) that the process can open and read to get 
> the output of «cmd». Similarly “>(«cmd»)” gets substituted with the name 
> of a file (i.e. not stdout) that the process can open and write to feed 
> input to waiting «cmd».
> 
> [...]