Robust Error Handling and Logging

#!/bin/bash

# --- Configuration ---
LOG_FILE="/tmp/myscript.log"

# --- Functions ---
# Log messages to stdout and file
log_message() {
  local TYPE="$1"
  local MESSAGE="$2"
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $TYPE: $MESSAGE" | tee -a "$LOG_FILE"
}

# Handle errors and exit
error_exit() {
  log_message "ERROR" "$1"
  exit 1
}

# --- Script Setup ---
# Exit immediately if a command exits with a non-zero status.
set -e

# Treat unset variables as an error when substituting.
set -u

# Use 'pipefail' to catch errors in pipes.
set -o pipefail

# --- Main Script Logic ---
log_message "INFO" "Script started."

# Example 1: A successful command
echo "Performing step 1..."
sleep 1
log_message "INFO" "Step 1 completed successfully."

# Example 2: A command that might fail
# Let's intentionally make 'cat' fail if the file doesn't exist
NON_EXISTENT_FILE="/tmp/this_file_does_not_exist_$(date +%s).txt"
log_message "INFO" "Attempting to read $NON_EXISTENT_FILE..."

# Use a subshell or check '$?' immediately after a potentially failing command
# if you don't want 'set -e' to exit prematurely, or if you want custom handling.
# For 'set -e' to work as expected, ensure the command is not part of a '&&' or '||' list,
# or the condition of an 'if' statement, unless you expect the error.

cat "$NON_EXISTENT_FILE" || error_exit "Failed to read $NON_EXISTENT_FILE"

# This line will not be reached if cat failed due to 'set -e' or 'error_exit'
log_message "INFO" "Script finished successfully."

exit 0