Unexpectedly using /bin/bash to execute a (startup) command on MacOS

[chernetskyi]

While debugging an issue I found out that Ghostty unconditionally uses /bin/bash to execute a (startup) command on MacOS. This came as a surprise to me after reading the documentation:

command

The command to run, usually a shell. If this is not an absolute path, it'll
be looked up in the PATH. If this is not set, a default will be looked up
from your system. The rules for the default lookup are:

• SHELL environment variable

• passwd entry (user information)

This can contain additional arguments to run the command with. If additional
arguments are provided, the command will be executed using /bin/sh -c.
Ghostty does not do any shell command parsing.

From the code, however, it's clear neither SHELL nor the passwd entry are respected:

ghostty/src/termio/Exec.zig

Line 1001 in 3f7c3af

try args.append("/bin/bash");

I suggest documenting this behavior to avoid further questions.

Now, personal story.

I use ZSH as my default/login shell on a Linux machine, but Ghostty launches fish. I keep my environment variables configuration in .zshenv to make them available to both POSIX-compliant shell scripts (executed by ZSH) and interactive sessions in fish (by inheriting variables from ZSH).

However, the same solution did not work on MacOS. Homebrew-installed fish failed to launch because PATH was not updated for /bin/bash.

The comments around those lines of code indicate that MacOS is a mess, but it would've been nice to have an option to change Bash to some other shell. For example, by switching to /bin/sh, which re-execs as Bash, Dash, or ZSH according to MacOS' man pages.

In the meantime, I'll consider moving my exports to .bash_profile because apparently Bash outperforms ZSH.

UPD: missed the --noprofile and --norc flags. Looks like the absolute path and environment variable duplication is the only way to go at the moment.