input.log with lines prefixed with [YYYY-MM-DD] > YYYY-MM-DD.log files, with entries for respective dates

split-log-by-date.sh

#!/bin/bash

# input:    log lines prefixed with "[YYYY-MM-DD" e.g. "[2024-02-13]", "[2024-02-13 00:00:41]" etc.
# output:   YYYY-MM-DD.log files, with entries for respective dates

# Input file
input_file=$1

gawk '
    # For each line
    {
        # Assume the date is in the format [YYYY-MM-DD] and time is HH:MM:SS, both in the first two fields
        # Extract the date directly without needing to trim brackets
        split($1, parts, /[-\[\]]/)
        year = parts[2]
        month = parts[3]
        day = parts[4]

        # Format the date to get the year, month, and day
        year_month_day = year "-" month "-" day

        # Write the line to the new file named after the date
        output_file = year_month_day ".log"
        print $0 >> output_file

        # Close the file to avoid too many open files
        close(output_file)
    }
' "$input_file"