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Format Reference

Quick reference for all formats supported by Kelora.

Input Formats

Specify input format with -f, --input-format <format>.

Overview

Format Description
auto Auto-detect from first line (default)
json Application logs, structured data (shorthand: -j)
line Unstructured logs, raw text
logfmt Heroku-style logs, simple structured logs
csv / tsv Spreadsheet data, exports
syslog System logs, network devices
combined Apache/Nginx web server access logs
cef ArcSight Common Event Format, SIEM data
cols:<spec> Custom column-based logs
regex:<pattern> Custom regex parsing with named groups and type annotations

JSON Format

Syntax: -f json or -j

Description: JSON Lines format (one object per line). Nested structures preserved.

Input Example: 

{"timestamp": "2024-01-15T10:30:00Z", "level": "ERROR", "service": "api", "message": "Connection failed"}

Output Fields: All JSON fields become event fields with original names and types.

Notes:

  • Use -M json for multi-line JSON objects
  • Preserves field types (strings, numbers, booleans, null)
  • Supports nested objects and arrays

Line Format

Syntax: -f line

Description: Plain text, one line per event.

Output Fields:

Field Type Description
line String Complete line content

Notes:

  • Auto-detect falls back to line when it can't identify a structured format
  • Empty lines are skipped
  • Useful for unstructured logs or custom parsing with --exec

Logfmt Format

Syntax: -f logfmt

Description: Heroku-style key-value pairs.

Input Example: 

timestamp=2024-01-15T10:30:00Z level=ERROR service=api message="Connection failed"

Output Fields: All key-value pairs become top-level fields.

Notes:

  • Supports quoted values: key="value with spaces"
  • Keys must be alphanumeric (with underscores/hyphens)

CSV / TSV Formats

Syntax:

  • -f csv - Comma-separated with header
  • -f tsv - Tab-separated with header
  • -f csvnh - CSV without header
  • -f tsvnh - TSV without header

Output Fields:

  • With header: Field names from header row
  • Without header: col_0, col_1, col_2, etc.

Type Annotations:

Specify field types for automatic conversion: 

kelora -f 'csv status:int bytes:int response_time:float' access.csv

Supported types: int, float, bool

Notes:

  • Quoted fields supported: "value, with, commas"
  • Escaped quotes: "value with ""quotes"""

Syslog Format

Syntax: -f syslog

Description: RFC5424 and RFC3164 syslog messages. Auto-detects format.

Input Examples:

RFC5424: 

<165>1 2024-01-15T10:30:00.000Z myhost myapp 1234 ID47 - Connection failed

RFC3164: 

<34>Jan 15 10:30:00 myhost myapp[1234]: Connection failed

Output Fields:

Field Type RFC5424 RFC3164 Description
pri Integer ✓ ✓* Priority value (facility * 8 + severity)
facility Integer ✓ ✓* Syslog facility code
severity Integer ✓ ✓* Severity level (0-7)
level String ✓ ✓* Log level (EMERG, ALERT, CRIT, ERROR, WARN, NOTICE, INFO, DEBUG)
ts String ✓ ✓ Parsed timestamp
host String ✓ ✓ Source hostname
prog String ✓ ✓ Application/program name
pid Integer/String ✓ ✓ Process ID (parsed as integer if numeric)
msgid String ✓ - Message ID
version Integer ✓ - Syslog protocol version
msg String ✓ ✓ Log message

*RFC3164: Only present if priority prefix <NNN> is included

Notes:

  • Severity levels: 0=emerg, 1=alert, 2=crit, 3=err, 4=warn, 5=notice, 6=info, 7=debug

Combined Log Format

Syntax: -f combined

Description: Apache/Nginx web server logs. Auto-handles three variants:

  • Apache Common Log Format (CLF)
  • Apache Combined Log Format
  • Nginx Combined with request_time

Input Examples:

Common: 

192.168.1.1 - user [15/Jan/2024:10:30:00 +0000] "GET /index.html HTTP/1.0" 200 1234

Combined: 

192.168.1.1 - user [15/Jan/2024:10:30:00 +0000] "GET /api/data HTTP/1.1" 200 1234 "http://example.com/" "Mozilla/5.0"

Nginx with request_time: 

192.168.1.1 - - [15/Jan/2024:10:30:00 +0000] "GET /api/data HTTP/1.1" 200 1234 "-" "curl/7.68.0" "0.123"

Output Fields:

Field Type Common Combined Nginx Description
ip String ✓ ✓ ✓ Client IP address
identity String ✓ ✓ ✓ RFC 1413 identity (omit if -)
user String ✓ ✓ ✓ HTTP auth username (omit if -)
ts String ✓ ✓ ✓ Request timestamp
request String ✓ ✓ ✓ Full HTTP request line
method String ✓ ✓ ✓ HTTP method (auto-extracted)
path String ✓ ✓ ✓ Request path (auto-extracted)
protocol String ✓ ✓ ✓ HTTP protocol (auto-extracted)
status Integer ✓ ✓ ✓ HTTP status code
bytes Integer ✓ ✓ ✓ Response size (omit if -, keep if 0)
referer String - ✓ ✓ HTTP referer (omit if -)
user_agent String - ✓ ✓ HTTP user agent (omit if -)
request_time Float - - ✓ Request time in seconds (omit if -)

Notes:

  • Parser auto-detects variant per line
  • Fields with - values omitted (except bytes includes 0)

CEF Format

Syntax: -f cef

Description: ArcSight Common Event Format for security logs.

Input Example: 

CEF:0|Security|threatmanager|1.0|100|worm successfully stopped|10|src=10.0.0.1 dst=2.1.2.2 spt=1232

Output Fields:

Syslog prefix (optional):

Field Type Description
ts String Timestamp from syslog prefix
host String Hostname from syslog prefix

CEF header:

Field Type Description
cefver String CEF format version
vendor String Device vendor name
product String Device product name
version String Device version
eventid String Event signature ID
event String Event name/classification
severity String Event severity (0-10)

Extensions: All extension key=value pairs become top-level fields with automatic type conversion (integers, floats, booleans)

Column Format

Syntax: -f 'cols:<spec>'

Description: Custom column-based parsing with whitespace (or custom separator) splitting.

Separator: Use --cols-sep <separator> for custom separators (default: whitespace)

Specification Syntax:

  • field - Consume one column
  • field(N) - Consume N columns and join
  • - or -(N) - Skip one or N columns
  • *field - Capture remaining columns (must be last)
  • field:type - Apply type annotation (int, float, bool, string)

Examples:

Simple fields: 

# Input: ERROR api "Connection failed"
kelora -f 'cols:level service *msg' app.log

Multi-token timestamp: 

# Input: 2024-01-15 10:30:00 INFO Connection failed
kelora -f 'cols:ts(2) level *msg' app.log --ts-field ts

Custom separator: 

# Input: name|age|city
kelora -f 'cols:name age:int city' --cols-sep '|' data.txt

Output Fields: Field names from specification with applied type conversions.

Notes:

  • *field must be the final token

Regex Format

Syntax: -f 'regex:<pattern>'

Description: Parse logs using regular expressions with named capture groups and optional type annotations.

Pattern Syntax:

  • (?P<name>pattern) - Named capture group (field stored as string)
  • (?P<name:type>pattern) - Named capture group with type annotation

Supported Types: int, float, bool (lowercase only)

Examples:

Simple extraction: 

# Input: 404 Not found
kelora -f 'regex:(?P<code:int>\d+) (?P<msg>.*)' app.log

Structured logs: 

# Input: 2025-01-15T10:00:00Z [ERROR] Database connection failed
kelora -f 'regex:^(?P<ts>\S+) \[(?P<level>\w+)\] (?P<msg>.+)$' app.log

Apache-style logs with typed fields: 

# Input: 192.168.1.1 - - [15/Jan/2025:10:00:00 +0000] "GET /api/users HTTP/1.1" 200 1234
kelora -f 'regex:^(?P<ip>\S+) - - \[(?P<timestamp>[^\]]+)\] "(?P<method>\w+) (?P<path>\S+) HTTP/[\d.]+" (?P<status:int>\d+) (?P<bytes:int>\d+)$' access.log

Output Fields: Field names from capture groups with applied type conversions.

Behavior:

  • Full-line matching: Pattern implicitly anchored with ^...$
  • Empty captures: Skipped (not stored as fields)
  • Non-matching lines:
    • Default (lenient): Returns error, line skipped, processing continues
    • With --strict: Returns error, processing halts
  • Type conversion failures (e.g., "abc" for :int):
    • Default (lenient): Automatically falls back to storing as string
    • With --strict: Returns error, processing halts

Reserved Field Names:

The following names cannot be used: original_line, parsed_ts, fields

Limitations:

  • Nested named capture groups are not supported
  • Type annotations must be lowercase (:int, not :INT)

Notes:

  • Use raw strings in shell to avoid escaping issues: -f 'regex:...'
  • Combine with --ts-field to specify which field contains the timestamp
  • Non-capturing groups (?:...) are supported

Auto-Detection

Syntax: -f auto

Description: Automatically detect format from first non-empty line.

Detection Order:

  1. JSON (starts with {)
  2. Syslog (starts with <NNN>)
  3. CEF (starts with CEF:)
  4. Combined (matches Apache/Nginx pattern)
  5. Logfmt (contains key=value pairs)
  6. CSV (contains commas with consistent pattern)
  7. Line (fallback)

Notes:

  • Detects once, applies to all lines
  • Not suitable for mixed-format files

Output Formats

Specify output format with -F, --output-format <format>.

Format Description
default Key-value format with colors
json JSON lines (one object per line)
logfmt Key-value pairs (logfmt format)
inspect Debug format with type information
levelmap Events grouped by log level
csv CSV with header row
tsv Tab-separated values with header row
csvnh CSV without header
tsvnh TSV without header

Use -q/--quiet to suppress output (implied by --stats and --metrics).

Levelmap Visual Example:

Levelmap output format showing compact log visualization

The levelmap format provides a compact visual representation of logs, showing timestamps and level indicators in a condensed format ideal for quick scanning.

Examples: 

kelora -j app.log -F json                      # Output as JSON
kelora -j app.log -F csv --keys ts,level,msg   # Output as CSV
kelora -j app.log --stats                      # Only stats

See Also