Shell

Shell é o programa que interpreta os comandos que você digita no terminal. Ele processa os comandos e chama programas.

Common shells:

• bash
• sh
• zsh
• fish

Types

Two independent axes that combine in any way.

Login vs Non-login

Whether this shell is the entry point for a new user session.

• Login shell - SSH, console login, su -
• Non-login shell - Opening a terminal tab inside an existing session

Interactive vs Non-interactive

Whether a human is typing commands.

• Interactive - You open a terminal and type
• Non-interactive - Running a script (bash script.sh)

Common combinations

Scenario	Type
SSH into a server	Interactive + Login
Open a terminal tab	Interactive + Non-login
Run a script	Non-interactive + Non-login

Bash startup files

Load order

Login shells — first match wins, rest are skipped:

1. /etc/profile
2. ~/.bash_profile → ~/.bash_login → ~/.profile (first found only)

Interactive non-login shells:

1. ~/.bashrc

User files

• Generic (read by any POSIX login shell — sh, dash, bash)

• ~/.profile: read if neither ~/.bash_profile nor ~/.bash_login exists

• Bash

• ~/.bash_profile: first choice for login shells; commonly sources ~/.bashrc so login shells also pick it up
• ~/.bash_login: read only if ~/.bash_profile is not found
• ~/.bashrc: read by interactive non-login shells

System files

• Generic
• /etc/environment: parsed by pam_env module (key=value pairs, not a shell script)
• /etc/profile: sourced by all login shells; loads /etc/profile.d/

• /etc/profile.d/: preferred location for system-wide environment variables

• Bash

• /etc/bashrc: sourced by interactive shells (/etc/bash.bashrc on Debian/Ubuntu)