hilighter

hilighter adds useful ANSI color to plain or noisy terminal text while behaving like a small Unix filter.

It reads stdin or text files, highlights every non-overlapping match, and writes the original text with ANSI styling added. Existing ANSI sequences are preserved.

Install

Requires Go 1.25 or newer.

go install github.com/erniebrodeur/hilighter/cmd/hilighter@latest

Usage

hilighter [-e <pattern> ...] [-t <theme>] [--] [file ...]
hilighter --help
hilighter --version

Highlight a command's output:

go test ./... 2>&1 | hilighter

Highlight one or more files in order:

hilighter application.log archive.log

With no file operands, hilighter reads stdin. A - operand reads stdin at that position, and -- permits dash-prefixed filenames:

hilighter before.log - after.log
hilighter -- -server.log

Use repeated -e flags to replace the configured and built-in rules with PCRE expressions. Expressions are evaluated in order and use the accent style:

some-command | hilighter -e '(?i)failed' -e '\b[1-9][0-9]* errors?\b'

Select a built-in theme with -t:

some-command | hilighter -t dark-plus

Or select a custom theme file:

some-command | hilighter -t themes/solarized.yaml

Relative theme paths resolve from ~/.hilighter.

Built-in themes

Hilighter ships 12 dark themes adapted from the palettes bundled with Visual Studio Code:

Theme	Selector
Abyss	abyss
Dark 2026	dark-2026
Dark Modern	dark-modern
Dark+	dark-plus
Default High Contrast	high-contrast
Kimbie Dark	kimbie-dark
Monokai, default	monokai
Monokai Dimmed	monokai-dimmed
Red	red
Solarized Dark	solarized-dark
Tomorrow Night Blue	tomorrow-night-blue
Visual Studio Dark	visual-studio-dark

Use a selector with -t or as the theme value in ~/.hilighter/config.yaml.

Default highlighting

When no expressions or custom rules are selected, the shipped rules highlight:

• IPv4, IPv6, and MAC addresses
• ISO 8601 and classic syslog timestamps
• URLs containing a scheme such as https://
• email addresses
• TRACE, DEBUG, INFO, NOTICE, WARN, WARNING, ERROR, and FATAL, case-insensitively

Earlier rules win when matches overlap. Every other non-overlapping occurrence is highlighted.

Configuration

On first run, hilighter creates:

~/.hilighter/
├── config.yaml
├── rules.yaml
└── themes/

The initial config.yaml selects the compiled Monokai theme:

theme: monokai

The initial rules.yaml is empty, which selects the shipped rules. A non-empty file replaces them. Rules use PCRE patterns and are evaluated in file order:

rules:
  - name: failure
    pattern: '(?i)failed'
    style: error

  - name: request
    pattern: '(GET|POST)\s+(\S+)'
    groups:
      "1": info
      "2": endpoint

  - name: warning-line
    pattern: '(?i)warning'
    scope: line
    style: warning

scope may be substring, the default, or line. groups maps capture-group numbers to semantic style names. See examples/rules/go-test.yaml for another rule set.

Custom themes overlay the built-in theme, so only changed styles need to be specified:

styles:
  error:
    fg: white
    bg: red
    bold: true
  endpoint:
    fg: cyan

Set the theme in config.yaml using a path relative to ~/.hilighter:

theme: themes/custom.yaml

Colors may be exact #RRGGBB truecolor values or the names black, blue, cyan, gray, green, magenta, orange, pink, red, white, and yellow. See examples/themes/default.yaml for a complete Monokai theme.

Rule-source precedence is repeated -e, then a non-empty ~/.hilighter/rules.yaml, then shipped rules. Theme precedence is -t, then config.yaml, then compiled Monokai.

Pipelines and errors

Preserve ANSI colors when paging:

some-command 2>&1 | hilighter | less -R

Input errors are written to stderr as they occur. Later file operands continue processing, and the final status is nonzero. Output errors stop processing immediately. A downstream broken pipe stops quietly without a redundant diagnostic and remains a nonzero exit.

hilighter processes text streams. Binary-file support is out of scope.

Version

hilighter --version

Source builds report hilighter-1.0.0:

go build -o hilighter ./cmd/hilighter
./hilighter --version

Update internal/cli/version.go when preparing each release.

License

Hilighter is licensed under GPL-3.0-only. Palette data adapted from Visual Studio Code retains its upstream MIT notice in THIRD_PARTY_NOTICES.md.