Re: < "$@" doesn't expand properly?

On Fri, Oct 3, 2025, at 6:47 PM, Marc Chantreux wrote:
> The simplest way to do it (I thought) was
>
> #!/bin/sh
> set -eux
> < "$@" | sponge "$1"
>
> so inplace counter awk '{$0+=2}1' would be expanded
> as
>
> < 'counter' 'awk' '{$0+=2}1' | sponge 'counter'
>
>
> but there is an error message
>
> ./inplace: 3: cannot open counter awk {$0+=2}1: No such file
>
> so it seems that the expansion leads to
>
> < 'counter awk {$0+=2}1' | sponge 'counter'
>
> is this an expected behavior?

POSIX leaves this unspecified.  Section 2.7 [1] says that field
splitting is not performed on the word following a redirection
operator, and section 2.5.2 [2] says that the expansion of "$@" is
unspecified in that context.

Almost no shell works the way you are expecting, except for zsh in
native mode (which I suspect is where you first tried this syntax):

	% cat /tmp/x.sh
	< "$@"
	% ./bash /tmp/x.sh a b
	/tmp/x.sh: line 1: "$@": ambiguous redirect
	% dash /tmp/x.sh a b
	/tmp/x.sh: 1: cannot open a b: No such file
	% ksh /tmp/x.sh a b
	/tmp/x.sh[1]: a b: cannot open [No such file or directory]
	% mksh /tmp/x.sh a b
	/tmp/x.sh[1]: can't open a b: No such file or directory
	% oksh /tmp/x.sh a b
	/tmp/x.sh[1]: cannot open a b: No such file or directory
	% yash /tmp/x.sh a b
	yash: redirection: cannot open file `a b': No such file or directory
	% zsh /tmp/x.sh a b
	/tmp/x.sh:1: no such file or directory: a
	% zsh --emulate sh /tmp/x.sh a b
	/tmp/x.sh:1: no such file or directory: a b

  [1] https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/utilities/V3_chap02.html#tag_19_07
  [2] https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/utilities/V3_chap02.html#tag_19_05_02

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vq