On Sun, Jun 18, 2017 at 02:02:05PM -0700, L A Walsh wrote:
[...]
> int dpi=$(ord $(<"$pixels_path" 2>/dev/null))
>
> This used to work but now works _unreliably_.
In what version does this used to work?
I tested on a couple of versions, and the behavior you describe didn't work:
dualbus@debian:~/src/gnu/bash-builds$ for b in bash-*/; do $b/bash -c 'echo
$(< <(echo x)) $BASH_VERSION'; done
x 3.2.57(1)-release
x 4.2.0(1)-release
x 4.2.53(1)-release
x 4.3.30(1)-release
dualbus@debian:~/src/gnu/bash-builds$ for b in bash-*/; do $b/bash -c 'echo
$(< <(echo x) >/dev/stdout) $BASH_VERSION'; done
3.2.57(1)-release
4.2.0(1)-release
4.2.53(1)-release
4.3.30(1)-release
And if you inspect the source code, you'll notice that this the command
substitution "cat file" functionality is implemented in here:
builtins/evalstring.c:
413 /* See if this is a candidate for $( <file ). */
414 if (startup_state == 2 &&
415 (subshell_environment & SUBSHELL_COMSUB) &&
416 *bash_input.location.string == '\0' &&
417 command->type == cm_simple && !command->redirects &&
418 (command->flags & CMD_TIME_PIPELINE) == 0 &&
419 command->value.Simple->words == 0 &&
420 command->value.Simple->redirects &&
421 command->value.Simple->redirects->next == 0 &&
422 command->value.Simple->redirects->instruction ==
r_input_direction &&
423 command->value.Simple->redirects->redirector.dest == 0)
424 {
425 int r;
426 r = cat_file (command->value.Simple->redirects);
427 last_result = (r < 0) ? EXECUTION_FAILURE :
EXECUTION_SUCCESS;
428 }
It's clear that the following conditions must be met:
- The redirection must be performed inside a command substitution (ln.
415)
- The command substitution must be a simple command (ln. 417)
- The simple command must consist of a single input redirection (ln.
420), i.e. no words (ln. 419), no "next" redirection (ln. 421), input
redirection (ln. 422), and the target being file descriptor 0 (ln.
423).
So that means that `echo $(<X 2>Y)' is not a valid "cat file" command
substitution.
I think that you're looking for:
$ bash -c 'printf "x\0y" > f; { a=$(<f); } 2>/dev/null; declare -p a'
declare -- a="xy"
Instead.
--
Eduardo Bustamante
https://dualbus.me/
