source Command in Linux: Run Scripts in the Shell

Quick take: The source command (or its shorthand .) runs a script in the current shell instead of a new one, so any variables, functions, or directory changes it makes persist. source ~/.bashrc reloads your shell configuration.

Introduction

Normally, running a script starts a new shell that exits when the script finishes, discarding any environment changes it made. The source command runs the script in your current shell instead, so its variables, functions, and aliases stick around. This is why you source ~/.bashrc to apply configuration changes without reopening the terminal.

Syntax

The basic syntax of the source command is:

source FILE [ARGUMENTS]
. FILE [ARGUMENTS]

Common Options and Parameters

The most useful options and parameters for the source command:

Practical Examples

Real source commands you can run today:

# Reload your shell configuration
source ~/.bashrc
# Shorthand with the dot
. ~/.bashrc
# Load environment variables from a file
source .env
# Load functions defined in a script
source ./functions.sh
# Activate a Python virtual environment
source venv/bin/activate

Tips and Best Practices

• Use source whenever a script must change your shell — set variables, define functions, or change directory — because a normal run cannot affect the parent shell.
• After editing ~/.bashrc or ~/.profile, source it to apply changes without logging out.
• Activating Python virtual environments relies on source — source venv/bin/activate modifies your current shell's PATH.

Final Thoughts

source runs a script in your current shell so its environment changes persist — the mechanism behind reloading ~/.bashrc, loading .env files, and activating virtual environments. Remember the single-dot shorthand (. file), and reach for source whenever a script needs to change the shell you are sitting in, not a throwaway child shell.