Failing script as process substitution not working in Dart

Question

Is there any way to make the script:

diff <(echo 'hello') <(echo 'hello-2')

work, as currently it fails with error in Dart when run using Process.run or Process.start:

syntax error near unexpected token `('

I tried to drill down on it and found out that since process substitution is not available when running the script through Process.run or Process.start, hence it's failing. So, is there any way to make it work?

I found out that we need to use set +o posix to make process substitution available if it's not, but I don't know how to do it in Dart.

I don't think its an `yq` issue, if it works as expected on the command line. You probably need to check with the melos part — Inian, Oct 25 '21 at 12:03
Yep, I found out about the root cause and have updated the question. Trying to find a solution for this. — Aakash, Oct 25 '21 at 16:37
Yes, so I wrapped the command in double quotes and it worked. — Aakash, Jan 03 '22 at 11:19
@Aakash not quite sure that I understood which part) do you have a code sample maybe?) — tatsuDn, Jan 03 '22 at 15:01
If that worked, it's because you ran it on a system where `sh` is a symlink to Bash, not because of any particular quoting. — tripleee, Apr 18 '22 at 15:18

score 0 · Answer 1 · answered Apr 18 '22 at 15:13

According to the documentation and common expectations, the shell will be /bin/sh; and so, you can't use Bash features like process substitutions.

You can always force it by running Bash explicitly:

Process.run("bash", ["-c", "diff <(echo 'hello') <(echo 'hello-2')"])

You could add set +o posix; to the beginning of the argument to bash -c (the argument can be an arbitrarily complex string with multiple commands) but of course, it's not necessary here, and actually a red herring in this context.

Here's an example of a slightly more complex command which uses the Bash-only "C-style" for loop syntax.

Process.run("bash", ["-c", "for ((i=0; i<=255; i++)); do ping -c 3 10.9.8.$i || break; done; echo 'finished'"])

... though generally speaking, it's probably better to keep your subprocesses as simple as possible, and write any necessary plumbing in the host language.

Perhaps see also Difference between sh and bash

Failing script as process substitution not working in Dart

1 Answers1