Detect when sh is actually bash

[Tyriar]

On my mac, sh is not a symlink, but it's actually bash when you do sh --help. This is fine as bash is POSIX compatible, but we should fix this shell type detection for this case so we don't lose shell integration.

[anthonykim1]

It seems like sh --help would still have access to shell integration, but not when we enter sh via entering sh in bash terminal.

I still see bash as shell type when I enter sh shell via typing sh in bash. I assume this fine as typing sh in bash is bash? I'm wondering if we just want to somehow use shellIntegration from bash in this case:

The tricky part is that as soon as we type 'sh' in bash in Mac, for example, the sh command does not finish until we exit. Terminal title never changes from bash either and we just show running sh.

Looking at environment variable specifically $SHELL, would not give us luck as it would just yield /bin/zsh for me regardless of whether I am in zsh, bash, or sh in Macbook ARM.

However running echo $0 (special shell parameter) yielded zsh, bash, or sh correctly.

I'm thinking two approaches here:

1. Watch for terminal event, such as window.onDidStartTerminalShellExecution, detect user is in bash, then also detect when user has ran sh on their terminal, then do something
2. Use the echo $0 via some hidden terminal?

[meganrogge]

@anthonykim1 I believe we are currently categorizing and treating sh as sh when it should be categorized and treated as bash, since it is that in reality.

Yes, we want to do this

if we just want to somehow use shellIntegration from bash in this case:

For me, echo $0 prints sh when in sh, which doesn't help us much

I think this line will verify that /bin/sh is actually bash

/bin/sh -c 'echo $BASH_VERSION'

with output 3.2.57(1)-release which confirms it's bash

[Tyriar]

We guess the shell type based on the executable here:

vscode/src/vs/workbench/contrib/terminal/browser/terminalInstance.ts

Lines 2759 to 2771 in 3962d9c

	const posixShellTypes: PosixShellType[] = [
	PosixShellType.Bash,
	PosixShellType.Csh,
	PosixShellType.Fish,
	PosixShellType.Ksh,
	PosixShellType.Sh,
	PosixShellType.Zsh,
	];
	for (const type of posixShellTypes) {
	if (exeBasename === type) {
	return type;
	}
	}

And then do it based on the title of the process here when it's running:

vscode/src/vs/platform/terminal/node/terminalProcess.ts

Lines 434 to 435 in 3962d9c

	const shellTypeValue = posixShellTypeMap.get(sanitizedTitle) || generalShellTypeMap.get(sanitizedTitle);
	this._onDidChangeProperty.fire({ type: ProcessPropertyType.ShellType, value: shellTypeValue });

So that should "self-heal" after it launches, and indeed my mac shows sh briefly as the terminal tab title followed by bash. But the SI script is determined before launch here based only on the executable file:

vscode/src/vs/platform/terminal/node/terminalEnvironment.ts

Lines 151 to 168 in 3962d9c

	// Linux & macOS
	switch (shell) {
	case 'bash': {
	if (!originalArgs || originalArgs.length === 0) {
	newArgs = shellIntegrationArgs.get(ShellIntegrationExecutable.Bash);
	} else if (areZshBashFishLoginArgs(originalArgs)) {
	envMixin['VSCODE_SHELL_LOGIN'] = '1';
	addEnvMixinPathPrefix(options, envMixin, shell);
	newArgs = shellIntegrationArgs.get(ShellIntegrationExecutable.Bash);
	}
	if (!newArgs) {
	return { type: 'failure', reason: ShellIntegrationInjectionFailureReason.UnsupportedArgs };
	}
	newArgs = [...newArgs]; // Shallow clone the array to avoid setting the default array
	newArgs[newArgs.length - 1] = format(newArgs[newArgs.length - 1], appRoot);
	envMixin['VSCODE_STABLE'] = productService.quality === 'stable' ? '1' : '0';
	return { type, newArgs, envMixin };
	}

We need some mechanism such as /bin/sh -c 'echo $BASH_VERSION' as @meganrogge suggested, but we need to run this before launching a terminal. Then cache the result at least for the lifetime of the pty host.

You'll also want to check on a Linux distro that doesn't set sh as bash. For example Debian WSL shows this for me: