fblog – view and filter JSON logs

fblog is a command-line application for viewing JSON-formatted logs. It focuses on turning structured log records into more readable output while retaining access to the individual fields contained in each JSON object.

The program attempts to identify common elements such as the message, severity and timestamp automatically. You can also select specific fields for display and customize how output is formatted. Nested values are supported and can be referenced in formatting expressions, while a collection of Handlebars helpers provides text styling, colors, case conversion and size formatting.

Filtering is one of fblog’s more powerful features. Filters are written using Lua expressions, allowing conditions to operate on fields from each JSON record. Nested JSON objects are converted into Lua records and arrays become Lua tables, so filters can work with structured data rather than treating an entire log entry as an opaque line of text.

fblog can also handle prefixed output produced when tools such as Kubernetes utilities combine logs from multiple pods. It supports message placeholder substitution, configurable mappings for log levels and shell completion generation. The default severity levels include trace, debug, info, warn, error and fatal, with corresponding colorization.

This is free and open source software.

Key Features

• Displays JSON-formatted log files.
• Automatically detects common message, severity and timestamp fields.
• Selects specific JSON fields for display.
• Filters records using Lua expressions.
• Supports nested JSON objects and arrays in filters.
• Customizes output using Handlebars templates.
• Provides text styling and color helpers.
• Colorizes common log severity levels.
• Maps custom log-level values to standard levels.
• Handles prefixed logs from multiple Kubernetes pods.
• Supports message placeholder substitution.
• Reads continuous log streams through standard input.
• Respects the NO_COLOR environment variable.
• Generates shell completions.

Website: github.com/brocode/fblog
Support:
Developer: Patrick Haun
License: WTFPL License

fblog is written in Rust. Learn Rust with our recommended free books and free tutorials.

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