スクリプトのベストプラクティスとLint

スクリプトのベストプラクティスが必要な理由

わかりやすさのためのコメント

#!/bin/bash
# This script demonstrates commenting best practices.
# Author: CoddyKit
# Date: 2023-10-27

# Function: greet_user
# Description: Prints a greeting message to the console.
# Arguments:
#   $1 - The name of the user to greet.
greet_user() {
  local name="$1" # Store the first argument in a local variable.
  echo "Hello, ${name}!" # Output the greeting message.
}

# Main script execution starts here.
echo "Script execution started."
greet_user "CoddyKit Learner" # Call the function with a specific name.
echo "Script execution finished."

明確な命名規則

一貫した書式とインデント

堅牢性: 'set -u'（nounset）

#!/bin/bash
# Demonstrating 'set -u' (nounset)

set -u # Exit if an unset variable is used

MY_GREETING="Hello"
echo "${MY_GREETING}, CoddyKit!"

# This variable is NOT set. With 'set -u', the script will exit here.
echo "Your name is: ${UNSET_NAME}" 

echo "This line will NOT be reached if 'set -u' is active and UNSET_NAME is indeed unset."

堅牢性: 'set -o pipefail'

#!/bin/bash
# Demonstrating 'set -o pipefail'

set -o pipefail # Ensures pipe's exit status is the last non-zero command

echo "Running a failing command in a pipe:"
echo "---"

# 'false' command always fails (exit status 1).
# 'cat /dev/null' always succeeds (exit status 0).
# With 'set -o pipefail', the pipe's overall exit status will be 1 from 'false'.
false | cat /dev/null

# This line will only be reached if the pipe above succeeds.
echo "---"
echo "Script finished successfully (this line won't show if pipe failed with set -o pipefail)."

ShellCheck の紹介

ShellCheck の動作を確認する: 悪いスクリプト

#!/bin/bash
# A script with some common issues

MY_NAME=coddykit # Variable assignment needs no space, but quoting is good for values
echo "Hello $MY_NAME!" # Missing quotes around variable expansion

if [ $1 = "admin" ]; then # Missing quotes around $1
  echo "Welcome, administrator."
fi

# A simple loop with potential issues
for file in *.txt; do # Unquoted glob could expand to multiple arguments
  echo File: $file # Missing quotes around $file
done

ShellCheckの警告を修正する

#!/bin/bash
# A script with issues fixed by ShellCheck

MY_NAME="CoddyKit" # Quote variable assignment values
echo "Hello ${MY_NAME}!" # Always quote variable expansions

if [ "$1" = "admin" ]; then # Quote positional parameters like $1
  echo "Welcome, administrator."
fi

# A simple loop with corrected quoting
for file in *.txt; do 
  echo "File: ${file}" # Quote variable expansions, especially in loops
done

ベストプラクティスの確認

振り返り：プロフェッショナルなスクリプト作成