Edit .bash_profile if it exists

[awelkie]

Fixes #883

[Diggsey]

Hi @awelkie, this looks great.

I would like to slightly alter the detection logic here, specifically:

• Modify .zprofile if either it already exists, or the shell is zsh
• Modify .bash_profile only if it exists, regardless of the current shell

IMO, this would provide the best result given each shell's profile logic.

However, I'd be happy to accept this PR as-is if you won't be able to make these changes, since it's a clear improvement over the status quo, and shouldn't cause any problems to tweak later.

[brson]

@Diggsey's suggestion sounds reasonable to me. Thanks @awelkie!

[awelkie]

I'll take a crack at making these changes. I would also like to add support for fish (#478). Should the logic there be to add add a file to ~/.config/fish/conf.d only if ~/.config/fish/ exists, regardless of the current shell?

[Diggsey]

@awelkie Thanks!

For all shells except bash, we should set their configuration if we detect their presence at all on the system. For the moment, the two detection methods we use are $SHELL and whether their configuration files are detected.

Bash is different, because it will fall back to .profile if .bash_profile does not exist, so even if $SHELL == "bash", we can't create .bash_profile if it doesn't already exist, as then bash would stop looking in .profile, which would break things for the user.

So for fish, we want to add a file to ~/.config/fish/conf.d if either the fish config directory already exists, or if fish is the current shell.

[awelkie]

I don't think I'll be able to get to the making the improvements for another few days, so feel free to merge this in if you want.

[brson]

For this PR I agree that at least it would be better to remove reading "SHELL" and just look for the presense of .bash_profile. zsh changes can be left for some other PR.

This should really also have a test case. Crib off of "install_adds_path_to_profile".

[brson]

I've updated this in #1179.