Linux: 環境変数とPATH — 開発環境の設定

http example.com
# Command 'http' not found

echo $PATH
# /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# ~/.local/bin is not in PATH, so the Shell can't find http
ls ~/.local/bin/http*
# /home/charlie/.local/bin/http

# Add ~/.local/bin to PATH
export PATH="$PATH:$HOME/.local/bin"
http example.com    # Now it works

# View all environment variables
printenv

# View individual variables
echo $HOME
echo $USER
echo $SHELL
echo $LANG
echo $PWD

# View current PATH
echo $PATH
# /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# Find which directory a command is in
which ls
# /usr/bin/ls

# View all possible locations for a command (including aliases and functions)
type ls
# ls is aliased to `ls --color=auto'

# Temporary setting (only effective in current Shell)
MY_VAR="hello"

# Export as environment variable (child processes can access it)
export MY_VAR="hello"

# Set and export in one command
export MY_VAR="hello"

# Unset an environment variable
unset MY_VAR

# Temporarily set for a single command (without polluting current environment)
LANG=ja_JP.UTF-8 date

Login Shell (SSH login, tty login):
    /etc/profile
    ~/.bash_profile   (if it exists, the following two are skipped)
    ~/.bash_login
    ~/.profile

Non-login Shell (opening a new terminal):
    /etc/bash.bashrc
    ~/.bashrc

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

# View environment variables
echo "My home directory is: $HOME"
echo "Current user: $USER"
echo "My Shell: $SHELL"

# Set a temporary variable
export GREETING="Hello from Linux"
echo $GREETING

# Open a new terminal window and check if $GREETING is still there
# Answer: No — temporary variables only exist in the current Shell

# View current PATH
echo $PATH | tr ':' '\n'    # Display one path per line

# Find which directory ls is loaded from
which ls
# /usr/bin/ls

# What happens if PATH is wrong?
PATH=""      # Clear PATH (dangerous!)
ls
# bash: ls: No such file or directory

# Restore PATH
export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

# Create your own scripts directory
mkdir -p ~/scripts

# Add ~/scripts to PATH (write to .bashrc)
echo 'export PATH="$PATH:$HOME/scripts"' >> ~/.bashrc

> 💡 ヒント：環境変数を永続化するには、`export`コマンドを`~/.bashrc`（または`~/.profile`）に書く必要があります。修正後は`source ~/.bashrc`で即座に反映。そうでなければ新しい設定は新しく開いたターミナルでのみ読み込まれます。

# Reload
source ~/.bashrc

# Verify
echo $PATH | tr ':' '\n' | grep scripts
# /home/alice/scripts

# Add the following to ~/.bashrc

# Default editor
export EDITOR=vim

# Locale
export LANG=en_US.UTF-8

# Python development
export PYTHONSTARTUP=~/.pythonrc    # Python interactive startup script
export PIP_REQUIRE_VIRTUALENV=true  # pip requires virtual environment

# Node.js development
export NODE_ENV=development
export npm_config_prefix=~/.npm-global

# Go development
export GOPATH=$HOME/go
export PATH="$PATH:$GOPATH/bin"

# Your own scripts
export PATH="$PATH:$HOME/scripts"
export PATH="$PATH:$HOME/.local/bin"

# Use which to find the command path
which python3
# /usr/bin/python3

# Use type to check command type (alias/function/builtin/external)
type ls
# ls is an alias for `ls --color=auto'
type cd
# cd is a shell builtin
type node
# node is /usr/bin/node

# Use command -v (most reliable method)
command -v python3
# /usr/bin/python3

#!/bin/bash
# debug-path.sh - Debug command-not-found issues

CMD="${1:-http}"

echo "=== 1. What is the command ==="
type "$CMD" 2>/dev/null || echo "type: $CMD not found"

echo ""
echo "=== 2. Which PATH directories contain this command ==="
IFS=':' read -ra PATHS <<< "$PATH"
for dir in "${PATHS[@]}"; do
    if [ -f "$dir/$CMD" ]; then
        echo "Found: $dir/$CMD"
    fi
done

echo ""
echo "=== 3. Global search with find ==="
find /usr /opt $HOME -name "$CMD" -type f 2>/dev/null | head -5

echo ""
echo "=== 4. If found but not in PATH ==="
echo "Run: export PATH=\"\$PATH:/found/directory\""