Pradeep's Knowledge Hub

Introduction

Shell profile files are scripts that configure your environment when a shell session starts. Understanding their execution order and purpose is essential for anyone working with UNIX/Linux systems.

Shell Types

• Login Shell: First shell after login (SSH, console, or bash --login).
• Non-login Interactive Shell: Terminal opened from GUI or bash without --login.
• Non-interactive Shell: Scripts or commands executed without user interaction.

Profile Files Overview

Common profile files include:

• /etc/profile – System-wide settings for login shells.
• ~/.profile – User-specific settings for POSIX shells.
• ~/.bash_profile – Bash login shell settings.
• ~/.bashrc – Bash interactive non-login shell settings.

Execution Precedence

The order in which files are read depends on the shell type:

Best Practices

• Do not mix shell-specific syntax in generic files like ~/.profile.
• Use ~/.bashrc for aliases and interactive settings.
• Source ~/.bashrc from ~/.bash_profile:

  if [ -f ~/.bashrc ]; then
      . ~/.bashrc
  fi

Forcing a Specific Shell

To change your login shell (requires root):

sudo chsh -s /bin/bash username

Without root, add this to ~/.profile:

if [ -x /bin/bash ]; then
    exec /bin/bash
fi

Key Things to Know

• Export environment variables in profile files for persistence.
• Append to PATH instead of overwriting it.
• Do not add writable directories to PATH for security.
• Bash supports advanced features like PROMPT_COMMAND and process substitution.