Tanguy Ortolo

Both Bash and Zsh use several startup scripts: profile, bashrc, zlogin, zshrc, etc.

The existence of several startup scripts exists to allow you to apply specific actions for interactive or login shells. For instance, you may want to set up a fancy colour prompt or to enable a powerful completion system for interactive shells only, as it would be pointless to apply it to non-interactive shells (that is, for shell scripts). Or you may want to display a joke and the weather forecast at login, but not each time you spawn a shell by other means.

Common

Both Bash and Zsh first execute a system-wide file, then the corresponding user-specific one. For instance, /etc/profile then ~/.profile. For simplicity I shall only mention the files' base names.

Bash

At startup, depending on the case:

• run as a login shell (or with the option --login), it executes profile (or bash_profile instead if it exists (only user-specific version));
• run as an interactive, non-login shell, it executes bashrc (the system-wide version is called bash.bashrc).

At exit, it executes ~/.bash_logout (the system-wide version is called bash.bash_logout).

Note the funny (read: insane) non-login condition for executing bashrc: it is often worked around by having the profile execute bashrc anyway.

Zsh

Zsh always executes zshenv. Then, depending on the case:

• run as a login shell, it executes zprofile;
• run as an interactive, it executes zshrc;
• run as a login shell, it executes zlogin.

At the end of a login session, it executes zlogout, but in reverse order, the user-specific file first, then the system-wide one, constituting a chiasmus with the zlogin files.

Summary

I personally find the Zsh process much saner. To be honest I should rather say that I find Bash's behaviour insane, with an absurd process (bashrc for interactive, non-login shells…) that needs to be worked around, and an inconsistent naming and search convention (~/.bashrc vs. /etc/bash.bashrc, no system-wide version of bash_logout).