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Comment by toastal | Hacker News Reader

The <() is a Bashism isn't it?

Yes. See "Process Substitution" in "man bash". It works great, e.g. with diff (or meld):

  # diff -u <(echo $'one\ntwo') <(echo one)
  --- /dev/fd/63  2020-08-13 16:14:44.449379498 +0200
  +++ /dev/fd/62  2020-08-13 16:14:44.450379506 +0200
  @@ -1,2 +1 @@
   one
  -two

Gotcha. I wanted to know if it was POSIX compliant (it wasn't clear to me last time I looked it up).

< is a redirect operator, the out of the item on the right is redirected to the in of the item on the left; () are just grouping operators like math to ensure that bit is self contained inline for the parser.

That might be a way to remember what it does, but I don't think that's how it works. Try doing `echo <(ls)` to see how it differs. Or, from the manpage:

> Process substitution is supported on systems that support named pipes (FIFOs) or the /dev/fd method of naming open files. It takes the form of <(list) or >(list). The process list is run with its input or output connected to a FIFO or some file in /dev/fd. The name of this file is passed as an argument to the current command as the result of the expansion. If the >(list) form is used, writing to the file will provide input for list. If the <(list) form is used, the file passed as an argument should be read to obtain the output of list.

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