スクリプトのエラー処理とログ出力

スクリプトの信頼性を高める

終了コードを理解する

#!/bin/bash
# This script demonstrates exit codes

echo "Attempting a successful command..."
ls /tmp
echo "Exit code for 'ls /tmp': $?"

echo

echo "Attempting a failing command..."
ls /nonexistent_directory
echo "Exit code for 'ls /nonexistent_directory': $?"

コマンドのステータスを確認する

#!/bin/bash
# Check if a file exists before trying to read it

FILENAME="test_file.txt"
touch $FILENAME # Create it for success case

if [ -f "$FILENAME" ]; then
  echo "File '$FILENAME' exists. Processing..."
  # ... do something with the file ...
  rm $FILENAME # Clean up
else
  echo "Error: File '$FILENAME' not found!"
  exit 1
fi

echo "Script finished."

<code>set -e</code>：エラー時に終了する

#!/bin/bash
set -e

echo "Starting important operations..."
mkdir my_temp_dir
cp /nonexistent_source my_temp_dir/target # This will fail

echo "This line will not be reached if cp fails."
rmdir my_temp_dir
echo "Script finished successfully."

クリーンアップに使う<code>trap</code>

#!/bin/bash

TEMP_DIR="/tmp/my_script_temp_$(date +%s)"

function cleanup {
  echo "Cleaning up temporary directory: $TEMP_DIR"
  rm -rf "$TEMP_DIR"
}

trap cleanup EXIT

mkdir "$TEMP_DIR"
echo "Working in $TEMP_DIR..."
# Simulate some work, maybe it fails
# cp /nonexistent_file "$TEMP_DIR/" # Uncomment to test failure

echo "Script completed."

出力をリダイレクトする

#!/bin/bash
# Redirect stdout to success.log and stderr to error.log

echo "This is a success message." > success.log
ls /nonexistent_path 2> error.log

echo "Check success.log and error.log files."
# To view them after running:
# cat success.log
# cat error.log

すべての出力を1つのファイルにまとめる

#!/bin/bash
# Redirect both stdout and stderr to a single log file

LOG_FILE="combined_script.log"

echo "Starting script..." &> "$LOG_FILE"
echo "This message goes to stdout." &>> "$LOG_FILE"
ls /nonexistent_dir 2>&1 | tee -a "$LOG_FILE"
echo "Script finished." &>> "$LOG_FILE"

echo "Check the '$LOG_FILE' file for all output."

ログにタイムスタンプを付ける

#!/bin/bash

LOG_FILE="timestamped_script.log"

function log_message {
  echo "$(date +%Y-%m-%d_%H:%M:%S) - $1" &>> "$LOG_FILE"
}

log_message "Script started."
sleep 1
log_message "Performing task A..."
# Simulate an error
ls /no_such_place || log_message "Error: Command failed."
sleep 1
log_message "Script finished."

echo "Check '$LOG_FILE' for timestamped entries."

<code>logger</code>でシステムログに送る

#!/bin/bash
# Send a message to system logs

SCRIPT_NAME="MyBackupScript"

logger -t "$SCRIPT_NAME" "Starting daily backup operation."

# Simulate a task
sleep 2
if [ $(($RANDOM % 2)) -eq 0 ]; then
  logger -t "$SCRIPT_NAME" -p user.info "Backup successful."
else
  logger -t "$SCRIPT_NAME" -p user.err "Backup failed: Disk full."
fi

echo "Messages sent to system logs. Check with 'journalctl -t $SCRIPT_NAME'."

エラー処理の確認

まとめと次のステップ