LOWDOWN-DIFF(1)

NAME
lowdown-diff - view differences in markdown files

SYNOPSIS
lowdown-diff [input_options] [output_options] [-s] [-M metadata] [-m metadata] [-o file] [-t mode] oldfile [newfile]

DESCRIPTION
Shows differences between lowdown(5) documents as formatted output. Results are written to standard output.

The short arguments are as follows:

-s  Produce a standalone document (e.g., a valid HTML document including document type, head, etc.) around the formatted content. See Standalone documents for details.

-M metadata
    Provide a single metadata key-value pair. This may be in the normal syntax or as pairs separated by an equal sign, depending upon which character (a colon or equal sign) comes first. Exits with an error if given neither. This overrides -m and what's parsed from the document. See Metadata.

-m metadata
    Like -M, but overridden by what's parsed the document, then -M.

-o file
    Send output to file unless it's “-”, in which case fall back to the default of standard output.

-t mode, -T mode
    The output mode. This may be html for HTML5 output, latex for LaTeX, gemini for the Gemini “gemtext” format, ms for roff output using the classic (i.e., no-extension) -ms package and needing table support, term for ANSI-compatible UTF-8 terminal output, man for roff output using the classic -man package, tree, to show the parse tree of the input document, and null to parse the document but do no rendering. See Output media. The -T mode form is retained for backward compatibility.

oldfile, newfile
    Markdown documents used for comparison. If newfile is not given or “-”, it is read from standard input.

The following are long options for input parsing. These affect the parse tree passed to all outputs.

--parse-hilite
    Enable highlight span support. This are disabled by default because it may be erroneously interpreted as section headers.

--parse-math
    Recognise mathematics equations.

--parse-maxdepth=depth
    The maximum depth of nested elements. This defaults to 128, which is probably more than enough for any real-world document. If the maximum is hit, the system exits as if memory were exhausted. Set to zero for no maximum.

--parse-no-autolink
    Do not parse http, https, ftp, mailto, and relative links or link fragments.

--parse-no-cmark
    Do not parse with CommonMark constraints. This also disables using the first ordered list value instead of starting all lists at one.

--parse-no-codeindent
    Do not parse indented content as code blocks.

--parse-no-callouts
    Do not parse GFM/MDN callouts (“admonitions”).

--parse-no-deflists
    Do not parse PHP extra definition lists.

--parse-no-ext-attrs
    Do not parse PHP extra extended attributes.

--parse-no-fenced
    Do not parse GFM fenced (language-specific) code blocks.

--parse-no-footnotes
    Do not parse MMD footnotes.

--parse-no-img-ext
    Deprecated. See --parse-no-ext-attrs.

--parse-no-intraemph
    Do not parse emphasis within words and links.

--parse-no-mantitle
    Do not parse manpage title, section, source, and volume from Pandoc title metadata. Manpages titles are indicated by a title then an open parenthesis, digit followed by optional characters, then a closed parenthesis.

--parse-no-metadata
    Do not parse metadata. This does not affect metadata given on -m or -M.

--parse-no-strike
    Do not parse strikethroughs.

--parse-no-super
    Do not parse super-scripts or sub-scripts at all.

--parse-no-tables
    Do not parse GFM tables.

--parse-no-tasklists
    Do not parse GFM task lists.

--parse-super-short
    If super-script parsing is enabled, use the traditional non-GFM “short” syntax.

There are many output long options. The following are shared by all output media:

--out-standalone
    Alias for -s.

--out-no-smarty
    Do not use the smart typography filter. By default, certain character sequences are translated into output-specific glyphs.

--template template
    When producing standalone -s output, use a template file. See Templates. Currently only for -tgemini, -thtml, -tlatex, -tman, -tms, and -ttree.

What follows are per-output long options. For HTML with -thtml, these are as follows:

--html-callout-mdn, --html-callout-gfm
    Output either or both MDN or GFM callout syntaxes.

--html-hardwrap
    Hard-wrap paragraph content by outputting line breaks where applicable.

--html-no-escapehtml
    If --html-no-skiphtml has been specified, this causes embedded HTML not to be escaped, and is instead output verbatim. This has no effect if --html-no-skiphtml has not been specified.

--html-no-head-ids
    Do not output id attributes for headers.

--html-no-num-ent
    Don't normalise HTML entities (when possible) as numeric ones and instead use the entities as given on input.

--html-no-owasp
    Don't follow the OWASP recommendations for escaping text, and do only the minimal escaping to make sure that regular content isn't interpreted as HTML.

--html-no-skiphtml
    Output embedded HTML. By default, embedded HTML is not output at all. See --html-no-escapehtml.

--html-titleblock
    If any were parsed, format the title information (title, author, date) into a header element appearing first in the document.

For both roff formats -tman and -tms (unless as noted), the following apply:

--roff-code-font=fonts
    Override the default constant-width fonts with a tuple of regular, bold, italic, and bold-italic variants in that order. For example, B,B,BI,BI uses bold (“B”) instead of a constant-width. Not specifying a font will use the default, as will specifying a zero-length font name. Aliases none, bold, and code set no special fonts, bold, and the default constant-width.

--roff-endnotes
    Delay printing of footnotes until the end of the document. Only applies to -tms, as -tman only supports endnotes.

--roff-no-numbered
    Don't output numbered headings ( .NH NN). Only applies to -tms.

--roff-no-skiphtml
    Output embedded HTML. This usually doesn't make sense because the HTML won't be interpreted by the output reader. By default, HTML is omitted.

--roff-no-links
    Don't show URLs for images and links (autolinks are still shown). (Link content is still shown.) Overrides --roff-short-links for images and links. Only applies when --roff-traditional is specified.

--roff-short-links
    Shorten URLs for images, links, and autolinks to only the domain name and final path. Only applies when --roff-traditional is specified.

--roff-traditional
    Don't use hyperlink macros ( .pdfhref, .UR, .MT), multi-page tables ( .TS H, .TH), Unicode sequence syntax ( \[uNNNN]), example block macros ( .EX), modern section headings ( .NH NN, .SH NN, .pdfhref O NN), or intra-document links ( .pdfhref L). The output is compatible with traditional troff(1).

The argument prefix --nroff, such as in --nroff-traditional, is deprecated in favour of --roff.

The -tterm output has the following:

--term-all-metadata
    If -s is specified, output all metadata instead of just the title, author, and date.

--term-columns=columns
    The number of columns in the terminal. Useful for when running in a pipe. Defaults to what the terminal reports or 72 if not in a terminal.

--term-hmargin=margin
    The number of left margin characters. Defaults to zero. Can also be auto to set the left margin to half the remaining --term-columns after subtracting --term-width.

--term-hpadding=padding
    The number of left padding characters. Defaults to four. Padding eats into --term-width.

--term-no-ansi
    Don't show ANSI styles at all. This implies --term-no-colour.

--term-no-colour
    Don't show ANSI colours. This will still decorate text with underlines, bolds, and italics, but not emit any colour codes.

--term-no-links
    Don't show URLs for images and links (autolinks are still shown). (Link content is still shown.) Overrides --term-shortlinks and --term-no-rellinks.

--term-no-rellinks
    Don't show URLs for relative links. (Link content is still shown.) Overrides --term-shortlinks.

--term-shortlinks
    Shorten URLs for images, links, and autolinks to only the domain name and final path.

--term-vmargin=margin
    The number of top and bottom margin newlines. Defaults to zero.

--term-width=width
    Soft limit on the number of characters per line including (--term-hpadding). This may be exceeded by literal text. If zero or unset, defaults to --term-columns or 80 at most. Truncates to --term-columns.

The -tgemini output has several flags that control the placement of links. By default, links (images, autolinks, and links) are queued when specified in-line then emitted in a block sequence after the nearest block element.

--gemini-link-end
    Emit the queue of links at the end of the document instead of after the nearest block element.

--gemini-link-inline
    Render all links within the flow of text. This will cause breakage when nested links, such as images within links, links in blockquotes, etc. It should not be used unless in carefully crafted documents.

--gemini-link-noref
    Do not format link labels. Takes precedence over --gemini-link-roman.

--gemini-link-roman
    When formatting link labels, use lower-case Roman numerals instead of the default lower-case hexavigesimal (i.e., “a”, “b”, ..., “aa”, “ab”, ...).

--gemini-metadata
    Print metadata as the canonicalised key followed by a colon then the value, each on one line (newlines replaced by spaces). The metadata block is terminated by a double newline. If there is no metadata, this does nothing.

The -tlatex output has the following options:

--latex-no-numbered
    Don't number sections (and subsections, etc.).

--latex-no-skiphtml
    Output embedded HTML. This usually doesn't make sense because the HTML won't be interpreted by the output reader. By default, HTML is omitted.

The -tfodt output has the following options:

--odt-no-skiphtml
    Output embedded HTML. This usually doesn't make sense because the HTML won't be interpreted by the output reader. By default, HTML is omitted.

--odt-style=file
    Specify an OpenDocument style file, which must consist of at least <office:font-face-decls>, <office:scripts>, and <office:styles> XML elements in the root of the document. This is not syntax-checked in any way.

  Output media
The output media is specified by -t, which defaults to -thtml.

-tfodt
    “Flat” OpenDocument output. Automatic styles (those conditional upon document state) are generated with output. Classes specified by PHP extended attributes are not checked for existence.

-tgemini
    Gemini “gemtext” format.

-thtml
    HTML5 output with UTF-8 encoding.

-tlatex
    Simple LaTeX output. The following packages are required: amsmath and amssymb for maths, graphicx for images, inputenc (utf8) for UTF-8 input, fontend (T1) and textcomp for output glyphs, lmodern for Latin modern font, xcolor for the difference engine output, and hyperref for links.

-tman
    The man macro package suitable for reading by groff(1), mandoc(1), Heirloom troff, or traditional troff(1). Does not support equations and images. Table support is provided by tbl(1). Since UTF-8 may be passed as input values, preconv(1) may need to be used.

-tms
    The ms macro package suitable for reading by groff(1) or traditional troff(1). Does not support equations and limited image support for encapsulated postscript (PS and EPS suffix) images. Images are always block-formatted. Image dimensions and extended attributes are ignored, though images are downsized if larger than the current text width. Table support is provided by tbl(1). Since UTF-8 may be passed as input values, preconv(1) may need to be used.

-tterm
    ANSI-escaped UTF-8 output suitable for reading on the terminal. Images and equations not supported.

-ttree
    Debugging output. Not for programmatic use, as the format may change between versions.

  Differences
The differences between old and new document are illustrated in the following ways:

-tfodt
    “Flat” Differences are rendered using document tracking.

-tgemini
    Differences are not rendered.

-tlatex
    Differences are rendered by colouring in blue (insert) and red (delete) (this format is not fixed).

-tman
    Differences are rendered by colouring in blue (insert) and red (delete) (this format is not fixed).

-tms
    Differences are rendered by colouring in blue (insert) and red (delete) (this format is not fixed).

-tterm
    Differences are rendered by background-colouring in blue (insert) and red (delete) (this format is not fixed).

-ttree
    Differences are manually in the tree output.

Differences in content metadata use the following rule: deleted metadata key-value pairs are not processed in the output, so only inserted or retained metadata are processed.

  Standalone documents
When -s is specified, the formatted content is serialised into a self-contained document template as defined by the output type.

If not explicitly set with --template, a default template is produced as follows:

-tfodt
    Envelope <office:document> and prologue <office:automatic-styles>, <office:master-styles>, and <office:body>.

-thtml
    HTML5 doctype declaration followed by envelope <html> with optional language, then <head>. In order, the <head> consists of charset and viewport <meta> elements; optional <meta> elements from metadata affiliation (creator), author, copyright, and date; optional CSS sources from metadata; optional JavaScript sources from metadata; the possibly-empty <title>; then optional arbitrary content from metadata HTML header.

-tlatex
    Prologue documentclass and usepackage statements, optional arbitrary content from metadata LaTeX header, then surrounding begin{document} statements.

-tman, -tms
    Prologue macros.

-tterm
    Prologue lines.

-ttree
    Metadata and parsed template.

See Metadata for metadata values used by the default template.

  Metadata
Metadata keys are canonicalised and de-deduplicated in the following order: -m (overridden by document content and -M), the prologue of the document itself, then -M (overriding document content and -m).

After de-duplication, metadata is serialised into document variables and/or standalone -s output.

When not using --template, the following metadata keys are used in the default -s template:

affiliation
    Author affiliation (organisation or institution). Multiple affiliations may be separated by two or more spaces (including newlines). Used in -thtml, -tlatex, and -tms.

author
    Document author. Multiple authors may be separated by two or more spaces (including newlines). Overridden by rcsauthor. Used in -tfodt, -thtml, -tlatex, -tms, and -tterm.

baseheaderlevel
    Added to each header level. Deprecated in favour of shiftheadinglevelby.

copyright
    A document copyright (without the word “Copyright”), for example, “2017, Kristaps Dzonsons”. Used in -tms and -thtml.

css A CSS file output in the HTML document head as a <link rel="stylesheet" href="..." /> statement. Multiple CSS files (in order) may be separated by two or more spaces (including newlines) and are output in the given order. Only used in -thtml.

date
    Document date in ISO-8601 YYYY-MM-DD format. Overridden by rcsdate. Used in -tfodt, -thtml, -tlatex, -tman, -tms, and -tterm.

htmlheader
    Arbitrary HTML content output in the HTML document head immediately prior to closing the head element. Only used in -thtml and with -s. This metadata is not processed: it's passed unchanged into the output.

javascript
    A JavaScript file output in the HTML document head as a <script src="..."></script> statement. Multiple script files (in order) may be separated by two or more spaces (including newlines) and are output in the given order. Only used in -thtml.

lang
    Document language in RFC 5646 format. Only used in -thtml.

latexheader
    Arbitrary LaTeX content output in the document prologue immediately prior to the begin{document}. Only used in -tlatex and with -s. This metadata is not processed: it's passed unchanged into the output.

manheader
    Arbitrary roff content output immediately prior to the .TH macro. Only used in -tman and with -s. This metadata is not processed: it's passed unchanged into the output.

msheader
    Arbitrary roff content output immediately prior to the .TL macro. Only used in -tms and with -s. This metadata is not processed: it's passed unchanged into the output.

rcsauthor
    Like author, but in RCS author format. Overrides author.

rcsdate
    Like date, but in RCS date format. Overrides date.

section
    Man page section, defaulting to “7”. Only used in -tman.

shiftheadinglevelby
    Shift all headers by the given number. For example, a value of 1 causes headers originally at level 1 (“<h1>”) to be level 2 (“<h2>”), while a value of -1 moves level 2 to 1. Levels will not move to less than 1. Takes precedence over baseheaderlevel. If unset or not a valid number, defaults to zero. Used in -tfodt, -thtml, -tlatex, -tman, and -tms.

source
    Man page source (organisation providing the manual). Only used in -tman.

volume
    Man page volume (describes the manual page section). Only used in -tman.

title
    Document title. Used in -tfodt, -thtml, -tlatex, -tman, -tms, and -tterm.

Default values, such “7” for the section, are not set as metadata values, and will not appear if the metadata key is used as a variable.

  Templates
Some output media accept a template (--template) to customise standalone (-s) output. Parsed input content is filled into templates through control statements that support conditionals, loops, and variable transformation sequences.

Control statements are delimited as $statement$ or ${statement}. Arbitrary white-space may surround the case-insensitive statement between matching delimiters. Statements without a closing delimiter are considered opaque text.

The following statements are available:

$$, ${}
    Output a literal $. This may contain arbitrary white-space.

$ifdef(expression)$
    Conditional statement. There may not be any white-space between the ifdef and the opening parenthesis. Begins a block that is ended by a else, endif, or the end of file. Its contents are output only if expression evaluates to a non-empty string.

$else$
    Begins a block that is ended by a endif or end of file. Its contents are output only if the condition of a preceding ifdef evaluates to an empty string. An else without a preceding ifdef is not output.

$endif$
    Closes a block begin with ifdef or else. If not preceded by one of those statements, is silently ignored.

$for(expression)$
    Looping statement. There may not be any white-space between the for and the opening parenthesis. Begins a block that is ended by an endfor or the end of file. Block contents contents are repeatedly output for each list item evaluated from expression. The anaphoric keyword this may be used to access the current loop expression within the block.

$expression$
    Replaced by the result of evaluating a template expression.

If a control statement ends with two consecutive hyphens before the closing delimiter, input is consumed up to and including the next newline or until end of file. This allows for line-sensitive output media to use control statements without superfluous blank lines.

Expressions consist of

    initial[([arg]*)]?[.transform[([arg]*)]?]*,

or an initial value accepting optional arguments followed by an optional series of transforms accepting optional arguments. If an argument list is empty or not provided, it evaluates to an empty list.

The initial value is one of the following:

and(expression[,expression]*)
    A non-empty list containing the value true if all expressions evaluate to non-empty lists, otherwise an empty list. An empty expression evaluates to an empty list.

"literal string"
    Evaluates to a singleton list containing the string. An empty string evaluates to an empty list. The double quote character may be escaped, such as "foo\"bar".

body
    The parsed input document body.

canonicalised metadata key
    The value for the given metadata key, if found, otherwise an empty list.

body
    The parsed input document body.

meta(key)
    Produce the metadata value for the canonicalised metadata key. Allows for keys that are also keywords like body or endif.

not(expression)
    A non-empty list containing the value true if the expression evaluates as an empty list, otherwise an empty list.

or(expression[,expression]*)
    A non-empty list containing the value true if one expression evaluates to non-empty lists, otherwise an empty list. An empty expression evaluates to an empty list.

this
    The value of a current loop context or an empty list.

If a metadata key is not specified in the input, or if the anaphoric this has not initialised by a looping context, the initial value evaluates to an empty list. Otherwise, the value is a singleton list.

If transforms are invalid, they will transform into an empty list.

The following transformations are available:

escapegemini, escapegeminiline
    Escape list items for gemini (-tgemini), either for multiple lines or compressed to a single line.

escapehtml, escapehtmlattr, escapehtmlurl
    Escape list items for HTML (-thtml) body content, attributes, and URL attributes, respectively.

escapelatex
    Escape list items for LaTeX (-tlatex) body content.

escaperoff, escaperoffline
    Escape list items for roff (-tms, -tman), either for multiple lines or compressed to a single line. escaperoff also escapes initial roff delimiters and those after newlines.

join
    Join a list into a singleton list using two spaces as a join delimiter.

lowercase
    Lowercase all list items.

split
    Split list items on sequences of two or more white-space tokens (space, newline, tab). This is usually invoked on a singleton, but may be repeatedly invoked on a pre-split list. Invokes trim prior to the first split. The resulting list has no items that are only white-space.

trim
    Trim white-space from the beginning and end of all list items. If an item has no non-white-space, it is discarded.

uppercase
    Uppercase all list items.

ENVIRONMENT

NO_COLOR
    Do not emit colours when in -tterm mode. Synonym for NO_COLOUR. Same as --term-nocolour.

FILES

share/html/default.html
    The default template used if --template is not provided to -thtml.

share/latex/default.latex
    The default template used if --template is not provided to -tlatex.

share/man/default.man
    The default template used if --template is not provided to -tman.

share/man/default.ms
    The default template used if --template is not provided to -tms.

share/odt/styles.xml
    Default styles used when generating standalone -tfodt documents. Template for --odt-style styles.

EXIT STATUS

EXAMPLES
To view Markdown differences on an ANSI-compatible, UTF-8 terminal:

    lowdown-diff -tterm old.md new.md | less -R

The terminal may also be used with groff(1) rendering:

    lowdown-diff -stms old.md new.md | \
      groff -itk -mspdf -Tutf8 | less -R
    lowdown-diff -stman old.md new.md | \
      groff -itk -man -Tutf8 | less -R

To emit a standalone HTML5 document:

    lowdown-diff -s old.md new.md > foo.html

To use groff(1) to format as a PS file:

    lowdown-diff -stms old.md new.md | \
      groff -itk -mspdf > foo.ps

Or with LaTeX:

    lowdown-diff -stlatex old.md new.md > foo.latex
    pslatex foo.latex

PDF generation follows similar logic:

    lowdown-diff -stms old.md new.md | \
      pdfroff -itk -mspdf > foo.pdf
    lowdown-diff -stlatex old.md new.md > foo.latex
    pdflatex foo.latex

UTF-8 support for groff(1) PDF or PS output requires appropriate fonts, such as the Unicode Times font. This and other Unicode fonts are not always installed by default. They may be found, for PDF output, in the devpdf set of the groff(1) font directory and are prefixed with ‘U’.

    lowdown-diff -stms old.md new.md | \
      pdfroff -itk -mspdf -FU-T > foo.pdf

SEE ALSO
lowdown(1), lowdown(3), lowdown(5)

AUTHORS
lowdown-diff was written by Kristaps Dzonsons, kristaps@bsd.lv.

CAVEATS
When viewing -tman differences with mandoc(1), the marker colours are not rendered. The -tgemini output also currently has no way of encoding differences.