log-merger 0.5.0
A command-line utility to display multiple log files, merged by log timestamp
Requires Python: >=3.9

# logmerger

`logmerger` is a TUI for viewing a merged display of multiple log files, merged by timestamp.

Given these two log files:

```
# log1.txt
2023-07-14 08:00:01 WARN   Connection lost due to timeout
2023-07-14 08:00:04 ERROR  Request processed unsuccessfully
Something went wrong
Traceback (last line is latest):
    blah
    blah
ValueError("shouldn't have done that")
2023-07-14 08:00:06 INFO   User authentication succeeded
2023-07-14 08:00:08 DEBUG  Starting data synchronization
2023-07-14 08:00:11 INFO   Processing incoming request
```

```
# log2.txt
2023-07-14 08:00:01 INFO   Request processed successfully
2023-07-14 08:00:03 INFO   User authentication succeeded
2023-07-14 08:00:06 DEBUG  Starting data synchronization
2023-07-14 08:00:08 INFO   Processing incoming request
2023-07-14 08:00:11 DEBUG  Performing database backup
2023-07-14 08:00:14 WARN   Invalid input received: missing required field
```
This command

    logmerger log1.txt log2.txt

Shows the following browsable merged display (enabled using the [textual](https://textual.textualize.io) Python library):

![Image](https://github.com/ptmcg/log_merger/blob/main/static/log1_log2_merged_tui_lr.jpg?raw=true)

Use `--output -` to send the merged logs to stdout:

```
  Timestamp                 Files/Log1.Txt                        Files/Log2.Txt
 ────────────────────────────────────────────────────────────────────────────────────────────────────
  2023-07-14 08:00:01.000   WARN   Connection lost due to         INFO   Request processed
                            timeout                               successfully
  2023-07-14 08:00:03.000                                         INFO   User authentication
                                                                  succeeded
  2023-07-14 08:00:04.000   ERROR  Request processed
                            unsuccessfully
                             Something went wrong
                             Traceback (last line is latest):
                                 blah
                                 blah
                             ValueError("shouldn't have done
                            that")
  2023-07-14 08:00:06.000   INFO   User authentication            DEBUG  Starting data
                            succeeded                             synchronization
  2023-07-14 08:00:08.000   DEBUG  Starting data                  INFO   Processing incoming request
                            synchronization
  2023-07-14 08:00:11.000   INFO   Processing incoming request    DEBUG  Performing database backup
                            INFO   Processing incoming request
                            (a little more...)
  2023-07-14 08:00:14.000   DEBUG  Performing database backup     WARN   Invalid input received:
                                                                  missing required field
```

## Installation

Install `logmerger` from PyPI (still using old project name `log_merger` for now):

    pip install log_merger

This will install `logmerger` as a shell/console command, so you can then run it directly without
invoking `python`.


## Command line arguments

`logmerger -h` will show the following help:

```
usage: logmerger [-h] [--interactive] [--output OUTPUT] [--start START] [--end END] [--width WIDTH]
                 [--line_numbers] [--csv CSV] [--encoding ENCODING]
                 [--timestamp_format [TIMESTAMP_FORMATS ...]] [--demo]
                 [files ...]

positional arguments:
  files                 log files to be merged

options:
  -h, --help            show this help message and exit
  --interactive, -i     show merged output using interactive TUI browser (default)
  --output OUTPUT, -o OUTPUT
                        save merged output to file ('-' for stdout; files ending in '.md' are saved
                        using Markdown)
  --start START, -s START
                        start time to select time window for merging logs
  --end END, -e END     end time to select time window for merging logs
  --width WIDTH, -w WIDTH
                        total screen width to use for interactive mode (defaults to current screen
                        width)
  --line_numbers, -ln   add line number column
  --csv CSV, -csv CSV   save merged logs to CSV file
  --encoding ENCODING, -enc ENCODING
                        encoding to use when reading log files (defaults to the system default encoding)
  --timestamp_format [TIMESTAMP_FORMATS ...]
                        custom timestamp format
  --demo                Run interactive demo
  
Start and end timestamps to clip the given files to a particular time window can be
given in `YYYY-MM-DD HH:MM:SS.SSS` format, with trailing milliseconds and seconds
optional, and "," permissible for the decimal point. A "T" can be included between
the date and time to simplify entering the timestamp on a command line (otherwise
would require enclosing in quotes because of the intervening space). These command
line values do not need to match the timestamp formats in the log files.

These values may also be given as relative times, such as "15m" for "15 minutes ago".
Valid units are "s", "m", "h", and "d".
```


## Supported file types

Log data is usually extracted from text log files, but can also be extracted
from other log related files.

| type                                                                               |                            |
|------------------------------------------------------------------------------------|----------------------------|
| text log files                                                                     | any file name ending       |
| text log files that have been gzip compressed (such as those created by logrotate) | filename ending in `.gz`   |
| packet capture files (experimental)                                                | filename ending in `.pcap` |


## Merging

Log files get merged by interleaving log lines from each based on timestamps in each log line. `logmerger` tries to 
use different timestamp formats until it finds a matching format for each input file. The supported formats are:

| format                       | description                                                                                         |
|------------------------------|-----------------------------------------------------------------------------------------------------|
| `YYYY-MM-DD HH:MM:SS,SSS`    | date+time to milliseconds, with ',' decimal (default for Python's `asctime` log marker)             |
| `YYYY-MM-DD HH:MM:SS.SSS`    | date+time to milliseconds, with '.' decimal                                                         |
| `YYYY-MM-DD HH:MM:SS`        | date+time to seconds                                                                                |
| `YYYY-MM-DDTHH:MM:SS,SSS`    | date+T+time to milliseconds, with ',' decimal                                                       |
| `YYYY-MM-DDTHH:MM:SS.SSS`    | date+T+time to milliseconds, with '.' decimal                                                       |
| `YYYY-MM-DDTHH:MM:SS`        | date+T+time to seconds                                                                              |
| `Jan DD HH:MM:SS`            | month/day + time (timestamp in syslog files); year is inferred from the create date of the log file |
| `DD/Jan/YYYY HH:MM:SS`       | day/month/year + time                                                                               |
| `DD/Jan/YYYY:HH:MM:SS ±ZZZZ` | day/month/year + time + timezone offset (converts timestamps to local time)                         |


Untimestamped log lines that contain multiple lines (such as a traceback) get combined with the previous timestamped
line (see in the example above).