Oil syntax for exec {fd}<file.txt

[andychu]

In other words, expose something like fd_state.Open(). You can't use plain open() because of the colliding file descriptor problem, discussed on PR #672 .

It should be scoped like shell's redirect and Python's with. So that means it involves Oil Blocks #631 .

---

I tried to use this syntax here:

https://github.com/oilshell/oil/blob/master/test/spec-runner.sh#L93

[andychu]

Maybe do something like perl:

https://perldoc.perl.org/functions/open

open '>' file.txt :out {  
  echo foo >& $out
}

[andychu]

If we wanted to be clever we could take 3 arguments at a time:

open \
  '<' input.txt :input \
  '>' output.txt :output {
  while true {
    read --line :line <& $input
    write --qsn $line >& $output
  }
}

Looks kind of ugly. This is the same:

open '<' input.txt :input  { 
  open '>' output.txt :output {
    while true {
      read --line :line <& $input
      write --qsn $line >& $output
    }
  }
}

I don't really like the quoted '>' but that's what Perl does ...
We could also do r and w like:

open output.txt w :out {
  open input.txt r :in {
     ....
  }
}

[andychu]

related to #841

[andychu]

I think the main use case for this is the #863 fopen builtin, we can get by without it for awhile ...