I recently stumbled upon a strange behavior in Bash that I'd love some clarity on. When I run this command: `a(`, I get an error saying `bash: syntax error near unexpected token 'newline'`. However, if I run `<(` after that, it prompts for more input. If I then abort it with Ctrl-C and run `a(` again, the error changes to `bash: syntax error near unexpected token 'newline' while looking for matching ')'`. This change in behavior is puzzling to me. It seems like Bash might be toggling some internal state when entering and exiting process substitutions. Can anyone explain this?
3 Answers
Yeah, Bash's handling of this is quirky! If you do something like `${` and hit Ctrl-C, you’ll see similar behavior, where the parser keeps looking for a `}`. In some other shells like Zsh and Fish, they clear the open state when you interrupt the command, making for a smoother experience.
You're kind of stuck in these nested subshells! When you hit Ctrl-C, it halts the inner command but not the command substitution itself. This behavior has been around for a while. The way Bash handles it might seem like a bug, but it doesn't mess with valid commands.
What you're experiencing isn't really a bug; it's more about how Bash manages its interactive parsing state. When you first run `a(`, Bash starts expecting a closing `)`, and that expectation lingers even after you've aborted a command. The syntax error messages reflect that expectation sticking around in the parser's context.
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