Login vs Non-Login, Interactive vs Non-Interactive

Two orthogonal axes

Every shell has two flags:

• Login or not — login shells are the first shell of a session: Terminal.app on open, ssh login, su -.
• Interactive or not — interactive shells have a prompt; non-interactive shells run scripts.

That gives 2x2 = four shell types, each loading a different set of config files.

The matrix (zsh)

Real-world cases

• Open Terminal.app → login + interactive (full reload).
• ssh user@host → login + interactive.
• ssh user@host 'echo hi' → login + non-interactive.
• Run ./script.sh from a session → non-login + non-interactive.
• Type zsh inside an existing zsh → non-login + interactive.
• cron / launchd jobs → non-login + non-interactive (.zshenv only).

Why this trips people up

You add export OPENAI_API_KEY=... to ~/.zshrc and it works in your terminal. Cron picks up your script and the variable is empty. Cron's shell is non-login + non-interactive, so .zshrc is skipped. Move the line to .zshenv (or have your script source the file explicitly).

Confirm at runtime

[[ -o login ]] && echo login. [[ -o interactive ]] && echo interactive. The flags are introspectable from inside the shell.