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# NAME

mdee - em·dee, Markdown Easy on the Eyes

# SYNOPSIS

    mdee [ options ] file ...

     -h  --help             show help
         --version          show version
     -d  --debug            debug level (repeatable)
     -x  --[no-]trace       trace mode (set -x)
     -n  --dryrun           dry-run mode
     -s  --style=#          output style (nup/pager/cat/filter/raw)
     -f  --filter           shortcut for --style=filter
     -p  --plain            shortcut for --style=pager
         --[no-]fold        line folding (default: on)
         --[no-]table       table formatting (default: on)
         --[no-]nup         nup paged output (default: on)
         --[no-]rule        use Unicode rules for tables (default: on)
     -w  --width=#          fold width (default: 80)
     -t  --theme=#[,#,...]  color theme(s) (default: hashed)
     -m  --mode=#           light or dark (default: light)
     -B  --base-color=#     override theme's base color
                            (e.g., Ivory, #780043, (120,0,67))
         --list-themes      list available themes
         --show=#           set field visibility (e.g., italic=1)
     -C  --pane=#           number of columns
     -R  --row=#            number of rows
     -G  --grid=#           grid layout (e.g., 2x3)
     -P  --page=#           page height in lines
     -S  --pane-width=#     pane width (default: 85)
    --bs --border-style=#   border style
         --[no-]pager[=#]   pager command

# VERSION

Version 0.14

# DESCRIPTION

**em·dee** (command: `mdee`) is a terminal-based multi-column
Markdown text viewer with syntax highlighting, particularly
useful for reading documents generated by LLMs.

It displays Markdown text as-is with minimal formatting: syntax
highlighting, line folding for long list items, and table column
alignment.  Markup characters (`**`, `` ` ``, `#`, etc.) are
preserved in the output.  By default, closing hashes are appended
to h3-h6 headers (via the built-in `hashed` theme) to make
heading levels visually distinct.  Link URLs are removed from the
display, showing only the link text (e.g., `[text](url)` becomes
`[text]`).  On terminals supporting OSC 8 hyperlinks, the link
text remains clickable.

It does not render Markdown into formatted output or reflow
paragraphs.  For full Markdown rendering, many other viewers are
available.  Combine them with [nup(1)](https://metacpan.org/pod/App%3A%3Anup) for similar paged output
(e.g., `nup glow README.md`).

The pipeline combines [greple(1)](https://metacpan.org/pod/App%3A%3AGreple) for colorization and
[nup(1)](https://metacpan.org/pod/App%3A%3Anup) for multi-column paged output.

Supported elements: headers (h1-h6), bold, italic, strikethrough,
inline code, code blocks, HTML comments, tables, and list items.

<div>
    <p><img width="750" src="https://raw.githubusercontent.com/tecolicom/App-mdee/main/images/3-column.png">
</div>

# INSTALLATION

## Homebrew

Use [tecolicom/tap](https://github.com/tecolicom/homebrew-tap):

    brew tap tecolicom/tap
    brew install app-mdee

## CPAN

    cpanm -n App::mdee

# OPTIONS

## General Options

- **-h**, **--help**

    Show help message.

- **--version**

    Show version.

- **-d**, **--debug**

    Set debug level.  Can be repeated for increasing verbosity.

    - `-d`

        Show theme values (`theme_light[]`/`theme_dark[]`) and pipeline
        stage names.  Output is in sourceable format that can be used in
        theme files or config.sh.

    - `-dd`

        Above, plus expanded color values (`colors[]`), pattern definitions
        (`pattern[]`), and full command lines for each pipeline stage.

- **-x**, **--trace**, **--no-trace**

    Enable or disable shell trace mode (`set -x`).  Useful for
    debugging script execution.  Can be toggled: `-x --no-x` enables
    then disables tracing.

- **-n**, **--dryrun**

    Dry-run mode. Show the pipeline without executing.
    With `-dd`, shows expanded command lines for each stage instead
    of function names.

## Processing Options

- **-s** _STYLE_, **--style**=_STYLE_

    Set the output style.  Default is `nup`.  Available styles:

    - `nup` - Full pipeline: fold + table + nup paged output (default)
    - `pager` - Fold + table, output to pager (`$PAGER` or `less`)
    - `cat` - Fold + table, output to stdout
    - `filter` - Table only (no fold, no nup), suitable for piping
    - `raw` - Highlight only (no fold, no table, no nup)

    The style sets the initial state of `--fold`, `--table`, and
    `--nup` options.  Subsequent options can override individual
    settings:

        mdee -s filter --fold file.md    # filter + fold
        mdee -p --no-fold file.md        # pager without fold

- **-f**, **--filter**

    Shortcut for `--style=filter`.  Reads from stdin (or files) and
    outputs highlighted Markdown to stdout.  Disables line folding and
    nup paged output, but keeps table formatting enabled.  Useful for
    piping Markdown content through mdee for syntax highlighting.

- **-p**, **--plain**

    Shortcut for `--style=pager`.  Enables fold and table formatting,
    outputs through a pager (`$PAGER` or `less`) instead of nup.

- **--\[no-\]fold**

    Enable or disable line folding for list items.  When enabled, long
    lines in list items are wrapped with proper indentation using
    [ansifold(1)](https://metacpan.org/pod/App%3A%3Aansifold).  Default is enabled.

    Supported list markers: `*`, `-`, `1.`, `1)`, `#.`, `#)`.
    The `#.` and `#)` forms are Pandoc's auto-numbered list syntax.

- **--\[no-\]table**

    Enable or disable table formatting.  When enabled, Markdown tables
    are formatted using [ansicolumn(1)](https://metacpan.org/pod/App%3A%3Aansicolumn) for aligned column display.
    Default is enabled.

- **--\[no-\]nup**

    Enable or disable [nup(1)](https://metacpan.org/pod/App%3A%3Anup) for multi-column paged output.  When
    disabled, output goes directly to stdout without formatting.
    Default is enabled.

- **--\[no-\]rule**

    Enable or disable Unicode rule characters for table borders.
    When enabled, ASCII pipe characters (`|`) are replaced with
    Unicode box-drawing characters (`│`, `├`, `┤`, `┼`) and
    dashes (`-`) in separator lines are replaced with horizontal
    rules (`─`).  Default is enabled.

- **-w** _N_, **--width**=_N_

    Set the fold width for text wrapping. Default is 80.
    Only effective when `--fold` is enabled.

## Theme Options

**em·dee** supports color themes for customizing syntax highlighting.
Themes define colors for various Markdown elements (headers, code blocks,
bold text, etc.).

- **-t** _NAME_, **--theme**=_NAME_\[,_NAME_,...\]

    Select color themes.  The default is `hashed`, which appends
    closing hashes to h3-h6 headers.

    Themes specified with `--theme` are added to the default, not
    replacing it.  Multiple themes can be specified as comma-separated
    names or by repeating the option.  Each theme is applied in order
    as a transformation:

        mdee --theme=warm file.md         # hashed (default) + warm
        mdee --theme=warm,hashed file.md  # same (hashed already in default)
        mdee --no-theme --theme=warm      # warm only (clear default first)
        mdee --no-theme file.md           # no theme

    Use `--no-theme` to clear the default theme.  It can be combined
    with `--theme` to start fresh.

    Theme files are searched in the following order:

    - 1. User theme directory: `${XDG_CONFIG_HOME:-~/.config}/mdee/theme/NAME.sh`
    - 2. Share theme directory: installed with the distribution under `auto/share/dist/App-mdee/theme/`

    Theme files are Bash scripts that modify `theme_light`,
    `theme_dark`, and/or `pattern[]` arrays directly:

        # theme/warm.sh — change base color
        theme_light[base]='<Coral>=y25'
        theme_dark[base]='<Coral>=y80'

        # theme/hashed.sh — append closing hashes to h3-h6
        for _mode in light dark; do
            declare -n _theme="theme_${_mode}"
            _theme[h3]+=';sub{s/(?<!#)$/ ###/r}'
            ...
        done

        # modify matching pattern
        pattern[link]='...'

    Use `-d` to dump current theme values in sourceable format.

- **-m** _MODE_, **--mode**=_MODE_

    Select light or dark mode.  Default is `light`.

    If the terminal supports background color detection (via
    [Getopt::EX::termcolor](https://metacpan.org/pod/Getopt%3A%3AEX%3A%3Atermcolor)), the mode is automatically selected based on
    terminal luminance.

    Each theme has light and dark variants optimized for different terminal
    backgrounds.  The built-in `default` theme uses RoyalBlue as the base
    color with automatic luminance adjustment:

    - `light` - RoyalBlue with luminance 25 (dark text for light backgrounds)
    - `dark` - RoyalBlue with luminance 80 (bright text for dark backgrounds)

- **-B** _COLOR_, **--base-color**=_COLOR_

    Override the theme's base color.  The base color determines the overall
    color scheme because all heading colors (h1, h2, h3, etc.) are derived
    from it by adjusting luminance.  For example, h2 might be `${base}+y20`
    (base color with luminance increased by 20).

    **Simple color name** - luminance is adjusted automatically:

    When you specify just a color name (without `<>` brackets or
    other syntax), the default luminance adjustment is applied based on
    the current mode:

        -B RoyalBlue          # becomes <RoyalBlue>=y25 in light mode
                              # becomes <RoyalBlue>=y80 in dark mode

    This makes it easy to try different colors without worrying about
    luminance values.  The default adjustments (`=y25` for light, `=y80`
    for dark) are designed to provide good contrast against typical terminal
    backgrounds.

    **Full color specification** - used exactly as specified:

    If you include `<>` brackets, luminance modifiers, or use RGB
    notation, the value is used as-is without any automatic adjustment:

        -B '<Ivory>'               # original color, no adjustment
        -B '<Ivory>=y50'           # explicit luminance 50
        -B '#780043'               # burgundy in hex
        -B '(120,0,67)'            # same color in RGB decimal

    **Customizing the default adjustment**:

    The automatic luminance adjustment values can be customized with the
    `--adjust` option:

        --adjust light='=y30'      # use =y30 instead of =y25 for light mode
        --adjust dark='=y70'       # use =y70 instead of =y80 for dark mode

    **Note**: Basic ANSI color codes (`R`, `G`, `B`, etc.) cannot be used
    because heading variations require luminance adjustment, which only works
    with full color specifications (X11 names, RGB hex, or RGB decimal).

- **--list-themes**

    List available themes with color samples and exit.

## Highlight Options

- **--show**=_FIELD_\[=_VALUE_\],...

    Control field visibility for highlighting.  Empty value or `0` disables
    the field; any other value (including `1`) enables it.

        --show italic           # enable italic
        --show bold=0           # disable bold
        --show all              # enable all fields
        --show all= --show bold # disable all, then enable only bold

    Multiple fields can be specified with commas or by repeating the option.
    The special field `all` affects all fields and is processed first.

    Available fields: `comment`, `bold`, `italic`, `strike`, `h1`,
    `h2`, `h3`, `h4`, `h5`, `h6`, `inline_code`, `code_block`,
    `link`, `image`, `image_link`.

    All fields are enabled by default.

## Layout Options (passed to nup)

- **-C** _N_, **--pane**=_N_

    Set the number of columns (panes).

- **-R** _N_, **--row**=_N_

    Set the number of rows.

- **-G** _CxR_, **--grid**=_CxR_

    Set grid layout. For example, `-G2x3` creates 2 columns and 3 rows.

- **-P** _N_, **--page**=_N_

    Set the page height in lines.

- **-S** _N_, **--pane-width**=_N_

    Set the pane width in characters. Default is 85.

- **--bs**=_STYLE_, **--border-style**=_STYLE_

    Set the border style.

## Pager Options

- **--\[no-\]pager**\[=_COMMAND_\]

    Set the pager command.  Use `--pager=less` to specify a pager,
    or `--no-pager` to disable paging.

# CONFIGURATION

User configuration is loaded from:

    ${XDG_CONFIG_HOME:-~/.config}/mdee/config.sh

This is a shell script that can set defaults and override colors:

    # ~/.config/mdee/config.sh
    default[mode]='dark'             # set default mode
    default[theme]='warm'            # set default theme(s)
    default[style]='pager'           # set default style
    default[width]=100               # set default fold width
    default[base_color]='DarkCyan'   # set default base color

The `default` associative array supports the following keys:

- `default[mode]` - Corresponds to `--mode` (e.g., `dark`, `light`)
- `default[theme]` - Corresponds to `--theme` (e.g., `warm`, `warm,hashed`)
- `default[style]` - Corresponds to `--style` (e.g., `pager`, `cat`)
- `default[width]` - Corresponds to `--width` (e.g., `100`)
- `default[base_color]` - Corresponds to `--base-color` (e.g., `DarkCyan`)

**Overriding theme colors and patterns**

Config.sh can modify theme arrays and patterns directly, using the
same mechanism as theme files:

    # Change base color for both modes
    theme_light[base]='<DarkCyan>=y25'
    theme_dark[base]='<DarkCyan>=y80'

    # Append to both light and dark using declare -n
    for _array in theme_light theme_dark; do
        declare -n _theme=$_array
        _theme[h3]+=';sub{s/(?<!#)$/ ###/r}'
    done

    # Modify matching patterns
    pattern[link]='...'

Since `${base}` references are expanded after loading, changing the
base color automatically affects all derived colors (h1, h2, bold, etc.).

Use `-d` to dump current theme and pattern values in sourceable format.

**Color specification format**

Color specifications use [Term::ANSIColor::Concise](https://metacpan.org/pod/Term%3A%3AANSIColor%3A%3AConcise) format.
The `FG/BG` notation specifies foreground and background colors
(e.g., `L25DE/${base}` means gray foreground on base-colored background).
The `${base}` string is expanded to the base color value after loading.

# EXAMPLES

    mdee README.md              # view markdown file
    mdee -C2 document.md        # 2-column view
    mdee -G2x2 manual.md        # 2x2 grid (4-up)
    mdee -w60 narrow.md         # narrower text width
    mdee --no-pager file.md     # without pager
    mdee --no-nup file.md       # output to stdout without nup
    mdee --no-fold file.md      # disable line folding
    mdee --no-table file.md     # disable table formatting

    # Output styles
    mdee -s pager file.md       # fold + table, output to pager
    mdee -s cat file.md         # fold + table, output to stdout
    mdee -s filter file.md      # table only, no fold/nup
    mdee -s raw file.md         # highlight only

    # Style shortcuts
    mdee -p file.md             # same as --style=pager
    cat file.md | mdee -f       # highlight stdin (filter mode)
    mdee -f file.md             # highlight only (no paging)

    # Override individual settings
    mdee -f --fold file.md      # filter + fold
    mdee -p --no-fold file.md   # pager without fold

    # Theme examples
    mdee --mode=dark file.md               # use dark mode
    mdee --mode=light file.md              # use light mode
    mdee -B Ivory file.md                  # override base color
    mdee --mode=dark -B '#780043' file.md  # dark mode with burgundy
    mdee --theme=warm file.md              # warm (Coral) base color
    mdee --theme=warm,hashed file.md      # warm + closing hashes
    mdee --list-themes                     # list available themes

# DEPENDENCIES

This command requires the following:

- [App::Greple](https://metacpan.org/pod/App%3A%3AGreple) - pattern matching and highlighting
- [App::Greple::tee](https://metacpan.org/pod/App%3A%3AGreple%3A%3Atee) - filter integration
- [App::ansifold](https://metacpan.org/pod/App%3A%3Aansifold) - ANSI-aware text folding
- [App::ansicolumn](https://metacpan.org/pod/App%3A%3Aansicolumn) - ANSI-aware column formatting
- [App::nup](https://metacpan.org/pod/App%3A%3Anup) - N-up multi-column paged output
- [App::ansiecho](https://metacpan.org/pod/App%3A%3Aansiecho) - ANSI color output
- [Getopt::Long::Bash](https://metacpan.org/pod/Getopt%3A%3ALong%3A%3ABash) - bash option parsing
- [Getopt::EX::termcolor](https://metacpan.org/pod/Getopt%3A%3AEX%3A%3Atermcolor) - terminal background detection

# IMPLEMENTATION

**em·dee** is implemented as a Bash script that orchestrates multiple
specialized tools into a unified pipeline.  The architecture follows
Unix philosophy: each tool does one thing well, and they communicate
through standard streams.

The overall data flow is:

    Input File
        |
        v
    [greple] --- Syntax Highlighting
        |
        v
    [ansifold] --- Text Folding (optional)
        |
        v
    [ansicolumn] --- Table Formatting (optional)
        |
        v
    [nup] --- Paged Output (nup style)
        |         or
    [pager] --- Pager Output (pager style)
        |
        v
    Terminal

## Pipeline Architecture

**em·dee** dynamically constructs a pipeline based on enabled options.
Each stage is defined as a Bash function (e.g., `run_greple`,
`run_fold`).  The `--dryrun` option displays the function-based
pipeline without execution.

### Processing Stages

The pipeline consists of four configurable stages.  Each stage can be
enabled or disabled independently using `--[no-]fold`, `--[no-]table`,
and `--[no-]nup` options.

#### Syntax Highlighting

The first stage uses [greple(1)](https://metacpan.org/pod/App%3A%3AGreple) with the `-G` (grep mode) and
`--ci=G` (capture index) options to apply different colors to each
captured group in regular expressions.

Supported Markdown elements:

- Headers (`# h1` through `###### h6`)
- Bold text (`**bold**` or `__bold__`)
- Italic text (`*italic*` or `_italic_`)
- Inline code (`` `code` ``)
- Code blocks (fenced with ```` ``` ```` or `~~~`)
- HTML comments (`<!-- comment -->`)

Code block detection follows the CommonMark specification:

- Opening fence: 0-3 spaces indentation, then 3+ backticks or tildes
- Closing fence: 0-3 spaces indentation, same character, same or more count
- Backticks and tildes cannot be mixed (```` ``` ```` must close with ```` ``` ````)

#### Text Folding

The second stage wraps long lines in list items using [ansifold(1)](https://metacpan.org/pod/App%3A%3Aansifold)
via [Greple::tee](https://metacpan.org/pod/Greple%3A%3Atee).  It preserves ANSI escape sequences and maintains
proper indentation for nested lists.

Recognized list markers include `*`, `-`, `1.`, `1)`, `#.`,
and `#)`.  The `#` marker is Pandoc's auto-numbered list syntax.

The folding width is controlled by `--width` option (default: 80).

#### Table Formatting

The third stage formats Markdown tables using [ansicolumn(1)](https://metacpan.org/pod/App%3A%3Aansicolumn).
Tables are detected by the pattern `^(\|.+\|\n){3,}` and formatted
with aligned columns while preserving ANSI colors.

### Output Stage

The final stage uses [nup(1)](https://metacpan.org/pod/App%3A%3Anup) to provide multi-column paged output.
Layout options (`--pane`, `--row`, `--grid`, `--page`) are passed
directly to nup.

## Theme System

**em·dee** implements a theme system where themes are transformations
applied to the built-in default theme.  Multiple themes can be
chained via `--theme=NAME1,NAME2,...`.

### Theme Structure

The built-in default theme is defined as `theme_light` and
`theme_dark` associative arrays.  Dark inherits undefined
keys from light immediately after declaration.  Theme files can
modify these arrays and the `pattern[]` array directly:

    # theme/warm.sh — change colors
    theme_light[base]='<Coral>=y25'
    theme_dark[base]='<Coral>=y80'

    # modify matching patterns
    pattern[link]='...'

#### Base Color Expansion

The `${base}` placeholder is expanded to the effective base color
after theme loading.  The base color is determined by the
`--base-color` option (default: RoyalBlue) with automatic luminance
adjustment based on mode (`=y25` for light, `=y80` for dark).

### Color Specifications

Colors are specified using [Term::ANSIColor::Concise](https://metacpan.org/pod/Term%3A%3AANSIColor%3A%3AConcise) format.
The `--cm` option maps colors to captured groups.  For example,
`L00DE/${base}` specifies gray foreground on base-colored background.

The color specification supports modifiers:

- `+y10` / `-y10`: Adjust luminance by percentage
- `=y50`: Set absolute luminance
- `D`: Bold, `U`: Underline, `E`: Erase line

### Terminal Mode Detection

**em·dee** uses [Getopt::EX::termcolor](https://metacpan.org/pod/Getopt%3A%3AEX%3A%3Atermcolor) to detect terminal background
luminance.  If luminance is below 50%, dark mode is automatically
selected.

# LIMITATIONS

## HTML Comments

Only HTML comments starting at the beginning of a line are highlighted.
Inline comments are not matched to avoid conflicts with inline code
containing comment-like text (e.g., `` `<!-->` ``).

## Emphasis

Emphasis patterns (bold and italic) do not span multiple lines.
Multi-line emphasis text is not supported.

## Links

Link patterns do not span multiple lines.  The link text and URL must
be on the same line.

Reference-style links (`[text][ref]` with `[ref]: url` elsewhere)
are not supported.

## OSC 8 Hyperlinks

Links are converted to OSC 8 terminal hyperlinks for clickable URLs:

- `[text](url)` - `[text]` links to url
- `![alt](url)` - `![alt]` links to url (image)
- `[![alt](img)](url)` - `!` links to img, `[alt]` links to url

This requires terminal support.  Compatible terminals include iTerm2,
Kitty, WezTerm, Ghostty, and recent versions of GNOME Terminal.
Apple's default Terminal.app does not support OSC 8.

When using `less` as pager, version 566 or later is required with
`-R` option.

For OSC 8 specification, see:
[https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda](https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda)

## Less Environment Variables

When `less` is used as pager (either directly via `--style=pager` or
through `nup`), the following environment variables affect behavior.
**mdee** sets defaults for these when they are not already defined:

- `LESS`

    Default: `-R`.  The `-R` option is required for ANSI color
    sequences to be displayed correctly.

- `LESSANSIENDCHARS`

    Default: `mK`.  This tells `less` to recognize ANSI sequences
    ending with `m` (SGR color) and `K` (erase line).  The erase line
    sequence is used for background color rendering.

If you already have these variables set in your environment, **mdee**
does not override them.

# SEE ALSO

[nup(1)](https://metacpan.org/pod/App%3A%3Anup), [greple(1)](https://metacpan.org/pod/App%3A%3AGreple), [ansifold(1)](https://metacpan.org/pod/App%3A%3Aansifold), [ansicolumn(1)](https://metacpan.org/pod/App%3A%3Aansicolumn)

# AUTHOR

Kazumasa Utashiro

# LICENSE

Copyright 2026 Kazumasa Utashiro.

This software is released under the MIT License.
[https://opensource.org/licenses/MIT](https://opensource.org/licenses/MIT)
