bash: command not found — how to fix

Quick Answer

# Check if the command exists anywhere on the system
which node           # shows path if found
command -v node      # POSIX-compatible version
type node            # also shows if it's an alias or function

# Check your PATH
echo $PATH

# If you just installed something, reload your shell config
source ~/.bashrc     # bash
source ~/.zshrc      # zsh

When this happens

bash: node: command not found
# or
zsh: command not found: python

The shell cannot find the program in any directory listed in $PATH.

Other causes & fixes

Add a directory to PATH

# Temporarily (current session only)
export PATH="$HOME/.local/bin:$PATH"

# Permanently — add to ~/.bashrc or ~/.zshrc
echo 'export PATH="$HOME/.local/bin:$PATH"' >> ~/.bashrc
source ~/.bashrc

Install the missing command (Ubuntu/Debian)

# Search for which package provides a command
apt-cache search node
sudo apt install nodejs

# Or use apt-file
sudo apt install apt-file
apt-file search bin/node

Version manager installed but not initialised

Tools like nvm, rbenv, pyenv need to be initialized in your shell profile.

# nvm — add to ~/.bashrc or ~/.zshrc
export NVM_DIR="$HOME/.nvm"
[ -s "$NVM_DIR/nvm.sh" ] && source "$NVM_DIR/nvm.sh"

# Then reload
source ~/.bashrc