Bash - バーン・アゲイン・シェル

Bash (Bourne Again Shell) は、GNU プロジェクトのために Brian Fox によって書かれた、Bourne シェルの無償ソフトウェア代替となる Unix シェルとコマンド言語です。1989年に最初にリリースされて以来、Bash はほとんどの Linux ディストリビューションのデフォルトシェルとなり、Unix/Linux エコシステムで最も広く使用されているシェルの1つです。元の Bourne シェルの機能に加えて、コマンド補完、コマンド履歴、改善されたスクリプト機能などの追加機能を組み合わせています。

インストールとセットアップ

Bash のインストール確認

# Check if Bash is installed
which bash
/bin/bash

# Check Bash version
bash --version
GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu)

# Check current shell
echo $SHELL
/bin/bash

# Check available shells
cat /etc/shells

デフォルトシェルとしての Bash の設定

# Set Bash as default shell for current user
chsh -s /bin/bash

# Set Bash as default shell for specific user (as root)
sudo chsh -s /bin/bash username

# Verify shell change
echo $SHELL

異なるシステムでの Bash のインストール

# Ubuntu/Debian
sudo apt update && sudo apt install bash

# CentOS/RHEL/Fedora
sudo dnf install bash

# macOS (using Homebrew for latest version)
brew install bash

# Arch Linux
sudo pacman -S bash

# FreeBSD
pkg install bash

基本的な Bash の構文とコマンド

コマンド構造

# Basic command structure
command [options] [arguments]

# Examples
ls -la /home
cp file1.txt file2.txt
grep -r "pattern" /path/to/search

変数と環境

# Variable assignment (no spaces around =)
name="John Doe"
age=30
path="/home/user"

# Using variables
echo $name
echo $\\\\{name\\\\}
echo "Hello, $name"

# Environment variables
export PATH="/usr/local/bin:$PATH"
export EDITOR="vim"

# Special variables
echo $0    # Script name
echo $1    # First argument
echo $#    # Number of arguments
echo $@    # All arguments
echo $    # Process ID
echo $?    # Exit status of last command

コマンド置換

# Using $() (preferred)
current_date=$(date)
file_count=$(ls|wc -l)
user_home=$(eval echo ~$USER)

# Using backticks (legacy)
current_date=`date`
file_count=`ls|wc -l`

# Nested command substitution
echo "Today is $(date +%A), $(date +%B) $(date +%d)"

引用符とエスケープ

# Single quotes (literal)
echo 'The variable $HOME is not expanded'

# Double quotes (variable expansion)
echo "Your home directory is $HOME"

# Escaping special characters
echo "The price is \$10"
echo "Use \"quotes\" inside quotes"

# Here documents
cat << EOF
This is a multi-line
text block that can contain
variables like $HOME
EOF

# Here strings
grep "pattern" <<< "$variable"

ファイル操作とナビゲーション

ディレクトリのナビゲーション

# Change directory
cd /path/to/directory
cd ~                    # Home directory
cd -                    # Previous directory
cd ..                   # Parent directory
cd ../..                # Two levels up

# Print working directory
pwd

# Directory stack operations
pushd /path/to/dir      # Push directory onto stack
popd                    # Pop directory from stack
dirs                    # Show directory stack

ファイルとディレクトリの一覧表示

# Basic listing
ls
ls -l                   # Long format
ls -la                  # Long format with hidden files
ls -lh                  # Human readable sizes
ls -lt                  # Sort by modification time
ls -lS                  # Sort by size
ls -lR                  # Recursive listing

# Advanced listing options
ls -la --color=auto     # Colored output
ls -la --time-style=full-iso  # ISO time format
ls -la --group-directories-first  # Directories first

ファイル操作

# Create files
touch file.txt
touch file1.txt file2.txt file3.txt

# Copy files and directories
cp source.txt destination.txt
cp -r source_dir/ destination_dir/
cp -p file.txt backup.txt    # Preserve attributes
cp -u source.txt dest.txt    # Update only if newer

# Move and rename
mv old_name.txt new_name.txt
mv file.txt /path/to/destination/
mv *.txt /path/to/directory/

# Remove files and directories
rm file.txt
rm -f file.txt              # Force removal
rm -r directory/            # Recursive removal
rm -rf directory/           # Force recursive removal
rm -i *.txt                 # Interactive removal

# Create directories
mkdir directory_name
mkdir -p path/to/nested/directory
mkdir -m 755 directory_name  # With specific permissions

ファイルのアクセス権と所有権

# Change permissions
chmod 755 file.txt
chmod u+x script.sh         # Add execute for user
chmod g-w file.txt          # Remove write for group
chmod o=r file.txt          # Set read-only for others
chmod -R 644 directory/     # Recursive permission change

# Change ownership
chown user:group file.txt
chown -R user:group directory/
chgrp group file.txt        # Change group only

# View permissions
ls -l file.txt
stat file.txt               # Detailed file information

テキスト処理と操作

ファイルコンテンツ操作

# View file contents
cat file.txt                # Display entire file
less file.txt               # Paginated view
more file.txt               # Simple paginated view
head file.txt               # First 10 lines
head -n 20 file.txt         # First 20 lines
tail file.txt               # Last 10 lines
tail -n 20 file.txt         # Last 20 lines
tail -f file.txt            # Follow file changes

# File comparison
diff file1.txt file2.txt
diff -u file1.txt file2.txt  # Unified format
cmp file1.txt file2.txt      # Binary comparison

テキスト検索とフィルタリング

# grep - pattern searching
grep "pattern" file.txt
grep -i "pattern" file.txt   # Case insensitive
grep -r "pattern" directory/ # Recursive search
grep -n "pattern" file.txt   # Show line numbers
grep -v "pattern" file.txt   # Invert match
grep -E "pattern1|pattern2" file.txt  # Extended regex

# Advanced grep options
grep -A 3 "pattern" file.txt # Show 3 lines after match
grep -B 3 "pattern" file.txt # Show 3 lines before match
grep -C 3 "pattern" file.txt # Show 3 lines around match
grep -l "pattern" *.txt      # Show only filenames
grep -c "pattern" file.txt   # Count matches

テキスト処理ツール

# sed - stream editor
sed 's/old/new/' file.txt           # Replace first occurrence
sed 's/old/new/g' file.txt          # Replace all occurrences
sed '1,5s/old/new/g' file.txt       # Replace in lines 1-5
sed '/pattern/d' file.txt           # Delete lines matching pattern
sed -n '1,10p' file.txt             # Print lines 1-10

# awk - pattern scanning and processing
awk '\\\\{print $1\\\\}' file.txt           # Print first column
awk '\\\\{print $NF\\\\}' file.txt          # Print last column
awk '/pattern/ \\\\{print $0\\\\}' file.txt # Print lines matching pattern
awk -F: '\\\\{print $1\\\\}' /etc/passwd    # Use : as field separator
awk '\\\\{sum += $1\\\\} END \\\\{print sum\\\\}' file.txt  # Sum first column

# cut - extract columns
cut -d: -f1 /etc/passwd             # Extract first field
cut -c1-10 file.txt                 # Extract characters 1-10
cut -f2,4 file.txt                  # Extract fields 2 and 4

# sort and uniq
sort file.txt                       # Sort lines
sort -n file.txt                    # Numeric sort
sort -r file.txt                    # Reverse sort
sort -k2 file.txt                   # Sort by second field
uniq file.txt                       # Remove duplicate lines
sort file.txt|uniq -c             # Count occurrences

入出力リダイレクションとパイプ

リダイレクション演算子

# Output redirection
command > file.txt              # Redirect stdout to file (overwrite)
command >> file.txt             # Redirect stdout to file (append)
command 2> error.log            # Redirect stderr to file
command 2>> error.log           # Redirect stderr to file (append)
command &> output.log           # Redirect both stdout and stderr
command > output.log 2>&1       # Redirect both stdout and stderr

# Input redirection
command < input.txt             # Read input from file
command << EOF                  # Here document
line 1
line 2
EOF

# Advanced redirection
command 3> file.txt             # Redirect to file descriptor 3
exec 3> file.txt                # Open file descriptor 3
echo "text" >&3                 # Write to file descriptor 3
exec 3>&-                       # Close file descriptor 3

パイプとコマンドチェーン

# Basic pipes
ls -l|grep "txt"              # List files and filter for .txt
ps aux|grep "process_name"    # Show processes and filter
cat file.txt|sort|uniq      # Sort and remove duplicates

# Complex pipe chains
cat /var/log/access.log|grep "404"|awk '\\\\{print $1\\\\}'|sort|uniq -c|sort -nr
find . -name "*.log"|xargs grep "ERROR"|cut -d: -f1|sort|uniq

# Tee command (split output)
command|tee file.txt          # Write to file and stdout
command|tee -a file.txt       # Append to file and stdout

プロセス管理

ジョブ制御

# Background and foreground jobs
command &                       # Run command in background
jobs                           # List active jobs
fg %1                          # Bring job 1 to foreground
bg %1                          # Send job 1 to background
kill %1                        # Kill job 1

# Process control signals
Ctrl+C                         # Interrupt (SIGINT)
Ctrl+Z                         # Suspend (SIGTSTP)
Ctrl+\                         # Quit (SIGQUIT)

プロセス情報

# Process listing
ps                             # Show current processes
ps aux                         # Show all processes
ps -ef                         # Full format listing
pstree                         # Show process tree
top                            # Real-time process monitor
htop                           # Enhanced process monitor

# Process management
kill PID                       # Terminate process
kill -9 PID                    # Force kill process
killall process_name           # Kill all processes by name
pkill pattern                  # Kill processes matching pattern
nohup command &                # Run command immune to hangups

Bash スクリプティングの基礎

スクリプト構造

Would you like me to continue with the remaining sections?```bash #!/bin/bash

Script description and metadata

Author: Your Name

Date: YYYY-MM-DD

Version: 1.0

Script content starts here

echo “Hello, World!”

```bash
# String variables
name="John Doe"
message='Hello, World!'
multiline="This is a
multi-line string"

# Numeric variables
number=42
pi=3.14159

# Arrays
fruits=("apple" "banana" "orange")
numbers=(1 2 3 4 5)

# Associative arrays (Bash 4+)
declare -A colors
colors[red]="#FF0000"
colors[green]="#00FF00"
colors[blue]="#0000FF"

# Array operations
echo $\\\\{fruits[0]\\\\}               # First element
echo $\\\\{fruits[@]\\\\}               # All elements
echo $\\\\{#fruits[@]\\\\}              # Array length
fruits+=("grape")               # Append element
```### 条件文
```bash
# if-then-else
if [ condition ]; then
    echo "Condition is true"
elif [ other_condition ]; then
    echo "Other condition is true"
else
    echo "No condition is true"
fi

# Test conditions
if [ "$var" = "value" ]; then          # String equality
if [ "$num" -eq 10 ]; then             # Numeric equality
if [ "$num" -gt 5 ]; then              # Greater than
if [ "$num" -lt 20 ]; then             # Less than
if [ -f "file.txt" ]; then             # File exists
if [ -d "directory" ]; then            # Directory exists
if [ -r "file.txt" ]; then             # File is readable
if [ -w "file.txt" ]; then             # File is writable
if [ -x "script.sh" ]; then            # File is executable

# Logical operators
if [ condition1 ] && [ condition2 ]; then    # AND
if [ condition1 ]||[ condition2 ]; then    # OR
if [ ! condition ]; then                     # NOT

# Case statement
case $variable in
    pattern1)
        echo "Matched pattern1"
        ;;
    pattern2|pattern3)
        echo "Matched pattern2 or pattern3"
        ;;
    *)
        echo "No pattern matched"
        ;;
esac
```### ループ
```bash
# for loop
for i in \\\\{1..10\\\\}; do
    echo "Number: $i"
done

for file in *.txt; do
    echo "Processing: $file"
done

for item in "$\\\\{array[@]\\\\}"; do
    echo "Item: $item"
done

# C-style for loop
for ((i=1; i<=10; i++)); do
    echo "Counter: $i"
done

# while loop
counter=1
while [ $counter -le 10 ]; do
    echo "Counter: $counter"
    ((counter++))
done

# until loop
counter=1
until [ $counter -gt 10 ]; do
    echo "Counter: $counter"
    ((counter++))
done

# Loop control
for i in \\\\{1..10\\\\}; do
    if [ $i -eq 5 ]; then
        continue    # Skip iteration
    fi
    if [ $i -eq 8 ]; then
        break      # Exit loop
    fi
    echo $i
done
```### 関数
```bash
# Function definition
function greet() \\\\{
    echo "Hello, $1!"
\\\\}

# Alternative syntax
greet() \\\\{
    echo "Hello, $1!"
\\\\}

# Function with return value
calculate_sum() \\\\{
    local num1=$1
    local num2=$2
    local sum=$((num1 + num2))
    echo $sum
\\\\}

# Function with local variables
process_file() \\\\{
    local filename=$1
    local line_count=$(wc -l < "$filename")
    echo "File $filename has $line_count lines"
\\\\}

# Function usage
greet "World"
result=$(calculate_sum 5 3)
echo "Sum: $result"
```## 高度なBashの機能
```bash
# Basic parameter expansion
echo $\\\\{variable\\\\}
echo $\\\\{variable:-default\\\\}       # Use default if unset
echo $\\\\{variable:=default\\\\}       # Set default if unset
echo $\\\\{variable:+alternate\\\\}     # Use alternate if set
echo $\\\\{variable:?error\\\\}         # Error if unset

# String manipulation
string="Hello, World!"
echo $\\\\{string#Hello\\\\}            # Remove shortest match from beginning
echo $\\\\{string##*/\\\\}              # Remove longest match from beginning
echo $\\\\{string%World!\\\\}           # Remove shortest match from end
echo $\\\\{string%%/*\\\\}              # Remove longest match from end
echo $\\\\{string/Hello/Hi\\\\}         # Replace first occurrence
echo $\\\\{string//l/L\\\\}             # Replace all occurrences

# Substring extraction
echo $\\\\{string:0:5\\\\}              # Extract substring (position:length)
echo $\\\\{string:7\\\\}                # Extract from position to end
echo $\\\\{#string\\\\}                 # String length
```### パラメータ展開
```bash
# Arithmetic expansion
result=$((5 + 3))
result=$((10 * 2))
result=$((20 / 4))
result=$((17 % 5))              # Modulo

# Increment/decrement
((counter++))
((counter--))
((counter += 5))
((counter -= 3))

# Arithmetic with variables
num1=10
num2=5
sum=$((num1 + num2))
product=$((num1 * num2))

# Floating point arithmetic (using bc)
result=$(echo "scale=2; 10/3"|bc)
result=$(echo "scale=4; sqrt(16)"|bc -l)
```### 算術演算
```bash
# Exit on error
set -e                          # Exit on any error
set -u                          # Exit on undefined variable
set -o pipefail                 # Exit on pipe failure

# Error handling in scripts
command||\\\\{
    echo "Command failed"
    exit 1
\\\\}

# Trap signals
trap 'echo "Script interrupted"; exit 1' INT TERM
trap 'cleanup_function' EXIT

# Function error handling
safe_command() \\\\{
    if ! command_that_might_fail; then
        echo "Error: Command failed" >&2
        return 1
    fi
\\\\}
```### エラーハンドリング
```bash
# System-wide configuration
/etc/bash.bashrc                # System-wide bashrc
/etc/profile                    # System-wide profile

# User-specific configuration
~/.bashrc                       # User's bashrc
~/.bash_profile                 # User's profile
~/.bash_login                   # Login shell configuration
~/.profile                      # POSIX shell profile
~/.bash_logout                  # Logout script
```## 設定とカスタマイズ
```bash
# ~/.bashrc example configuration

# Source global definitions
if [ -f /etc/bashrc ]; then
    . /etc/bashrc
fi

# User specific environment
export EDITOR="vim"
export BROWSER="firefox"
export PAGER="less"

# Custom PATH
export PATH="$HOME/bin:$HOME/.local/bin:$PATH"

# Aliases
alias ll='ls -alF'
alias la='ls -A'
alias l='ls -CF'
alias grep='grep --color=auto'
alias fgrep='fgrep --color=auto'
alias egrep='egrep --color=auto'

# Custom functions
mkcd() \\\\{
    mkdir -p "$1" && cd "$1"
\\\\}

extract() \\\\{
    if [ -f $1 ] ; then
        case $1 in
            *.tar.bz2)   tar xjf $1     ;;
            *.tar.gz)    tar xzf $1     ;;
            *.bz2)       bunzip2 $1     ;;
            *.rar)       unrar e $1     ;;
            *.gz)        gunzip $1      ;;
            *.tar)       tar xf $1      ;;
            *.tbz2)      tar xjf $1     ;;
            *.tgz)       tar xzf $1     ;;
            *.zip)       unzip $1       ;;
            *.Z)         uncompress $1  ;;
            *.7z)        7z x $1        ;;
            *)     echo "'$1' cannot be extracted via extract()" ;;
        esac
    else
        echo "'$1' is not a valid file"
    fi
\\\\}

# Prompt customization
PS1='\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

# History configuration
HISTSIZE=10000
HISTFILESIZE=20000
HISTCONTROL=ignoredups:ignorespace
shopt -s histappend

# Shell options
shopt -s checkwinsize
shopt -s globstar
shopt -s cdspell
```### Bashの設定ファイル
```bash
# Set options
set -o vi                       # Vi editing mode
set -o emacs                    # Emacs editing mode (default)
set -o noclobber                # Prevent file overwriting
set +o noclobber                # Allow file overwriting

# Shopt options
shopt -s autocd                 # Auto cd to directory
shopt -s cdspell                # Correct minor spelling errors
shopt -s checkwinsize           # Update LINES and COLUMNS
shopt -s cmdhist                # Save multi-line commands
shopt -s dotglob                # Include hidden files in globbing
shopt -s expand_aliases         # Expand aliases
shopt -s extglob                # Extended globbing
shopt -s globstar               # ** recursive globbing
shopt -s histappend             # Append to history file
shopt -s nocaseglob             # Case-insensitive globbing
```### .bashrcのカスタマイズ
```bash
# Emacs mode (default)
Ctrl+A                          # Beginning of line
Ctrl+E                          # End of line
Ctrl+B                          # Back one character
Ctrl+F                          # Forward one character
Alt+B                           # Back one word
Alt+F                           # Forward one word
Ctrl+D                          # Delete character
Ctrl+H                          # Backspace
Ctrl+K                          # Kill to end of line
Ctrl+U                          # Kill to beginning of line
Ctrl+W                          # Kill previous word
Alt+D                           # Kill next word
Ctrl+Y                          # Yank (paste)
Ctrl+T                          # Transpose characters
Alt+T                           # Transpose words

# Vi mode
set -o vi
Esc                             # Enter command mode
i                               # Insert mode
a                               # Append mode
A                               # Append at end of line
I                               # Insert at beginning of line
```### Bashのオプションと設定
```bash
# History commands
history                         # Show command history
history 10                      # Show last 10 commands
history -c                      # Clear history
history -d 5                    # Delete history entry 5

# History expansion
!!                              # Previous command
!n                              # Command number n
!string                         # Last command starting with string
!?string                        # Last command containing string
^old^new                        # Replace old with new in previous command

# History search
Ctrl+R                          # Reverse search
Ctrl+S                          # Forward search
Ctrl+G                          # Cancel search

# History configuration
export HISTSIZE=10000           # Commands in memory
export HISTFILESIZE=20000       # Commands in file
export HISTCONTROL=ignoredups   # Ignore duplicates
export HISTIGNORE="ls:ll:cd:pwd:bg:fg:history"  # Ignore commands
export HISTTIMEFORMAT="%F %T "  # Add timestamps
```## コマンドライン編集と履歴
```bash
# Debug modes
bash -x script.sh               # Execute with trace
bash -n script.sh               # Check syntax without execution
bash -v script.sh               # Verbose mode

# Debug options in script
set -x                          # Enable trace
set +x                          # Disable trace
set -v                          # Enable verbose
set +v                          # Disable verbose

# Conditional debugging
if [ "$DEBUG" = "1" ]; then
    set -x
fi

# Debug function
debug() \\\\{
    if [ "$DEBUG" = "1" ]; then
        echo "DEBUG: $*" >&2
    fi
\\\\}
```### コマンドライン編集
```bash
# Check command success
if command; then
    echo "Command succeeded"
else
    echo "Command failed"
fi

# Check exit status
command
if [ $? -eq 0 ]; then
    echo "Success"
else
    echo "Failed with exit code $?"
fi

# Validate input
if [ $# -ne 2 ]; then
    echo "Usage: $0 <arg1> <arg2>"
    exit 1
fi

# Check file existence
if [ ! -f "$filename" ]; then
    echo "Error: File $filename does not exist"
    exit 1
fi
```### 履歴管理
```bash
# Time command execution
time command
time \\\\{ command1; command2; \\\\}

# Profile script execution
PS4='+ $(date "+%s.%N"): '
set -x
# Your commands here
set +x

# Memory usage
/usr/bin/time -v command

# Disk usage
du -sh directory/
df -h
```## デバッグとトラブルシューティング
```bash
# Use full paths for commands
/bin/ls instead of ls
/usr/bin/find instead of find

# Validate input
case "$input" in
    [a-zA-Z0-9]*)
        # Valid input
        ;;
    *)
        echo "Invalid input"
        exit 1
        ;;
esac

# Quote variables
rm "$filename"                  # Correct
rm $filename                    # Dangerous

# Use arrays for file lists
files=( *.txt )
for file in "$\\\\{files[@]\\\\}"; do
    process "$file"
done
```### スクリプトのデバッグ
```bash
# Use built-in commands when possible
[[ condition ]]                 # Instead of [ condition ]
(( arithmetic ))                # Instead of [ arithmetic ]

# Avoid unnecessary subshells
var=$(cat file)                 # Subshell
var=$(<file)                    # Built-in

# Use parameter expansion
$\\\\{var#pattern\\\\}                  # Instead of sed/awk for simple operations
$\\\\{var%pattern\\\\}
$\\\\{var/pattern/replacement\\\\}

# Efficient loops
while IFS= read -r line; do     # Read file line by line
    process "$line"
done < file.txt
```### エラーチェック
```bash
# Use functions for repeated code
log_message() \\\\{
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" >&2
\\\\}

# Separate configuration
CONFIG_FILE="$\\\\{HOME\\\\}/.myapp.conf"
if [ -f "$CONFIG_FILE" ]; then
    source "$CONFIG_FILE"
fi

# Use meaningful variable names
user_count=10                   # Good
uc=10                          # Poor

# Comment complex logic
# Calculate the number of days between two dates
start_date=$(date -d "$1" +%s)
end_date=$(date -d "$2" +%s)
days=$(( (end_date - start_date) / 86400 ))
```### パフォーマンス監視