.\" Copyright (c) Kristaps Dzonsons <kristaps@bsd.lv>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
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.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate$
.Dt LOWDOWN-DIFF 1
.Os
.Sh NAME
.Nm lowdown-diff
.Nd view differences in markdown files
.Sh SYNOPSIS
.Nm lowdown-diff
.Op input_options
.Op output_options
.Op Fl s
.Op Fl M Ar metadata
.Op Fl m Ar metadata
.Op Fl o Ar file
.Op Fl t Ar mode
.Ar oldfile
.Op Ar newfile
.Sh DESCRIPTION
Shows differences between
.Xr lowdown 5
documents as formatted output.
Results are written to standard output.
.Pp
The arguments are as follows:
.Bl -tag -width Ds
.It Fl s
Standalone mode.
This emits a document envelope surrounding the output by drawing from
document metadata.
See
.Sx Metadata
on providing information to the document envelope.
This applies to
.Fl t Ns Ar gemini ,
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
.Fl t Ns Ar ms ,
.Fl t Ns Ar man ,
and
.Fl t Ns Ar fodt .
.It Fl M Ar metadata
Provide a single metadata key-value pair.
This may be in the syntax specified by
.Xr lowdodwn 5
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 colon nor equal sign.
May be invoked multiple times for each pair.
This overrides
.Fl m
and what's parsed from the document.
.It Fl m Ar metadata
Like
.Fl M ,
but is overridden by what's parsed the document, then
.Fl M .
.It Fl o Ar file
Send output to
.Ar file
unless it's
.Dq - ,
in which case fall back to the default of standard output.
.It Fl t Ar mode , Fl T Ar mode
The output mode.
This may be
.Ar html
for HTML5 output,
.Ar latex
for LaTeX,
.Ar gemini
for the Gemini format,
.Ar ms
for roff output using the classic (i.e., no-extension)
.Fl ms
package and needing table support,
.Ar term
for ANSI-compatible UTF-8 terminal output,
.Ar man
for roff output using the classic
.Fl man
package,
.Ar tree ,
to show the parse tree of the input document, and
.Ar null
to parse the document but do no rendering.
See
.Sx Output modes .
The
.Fl T Ar mode
form is retained for backward compatibility.
.It Ar oldfile , newfile
Markdown documents used for comparison.
If
.Ar newfile
is not given or
.Dq - ,
it is read from standard input.
.El
.Pp
The following are options for input parsing.
These affect the parse tree passed to all outputs.
.Bl -tag -width Ds
.It Fl -parse-hilite
Enable highlight span support.
This are disabled by default because it may be erroneously interpreted
as section headers.
.It Fl -parse-math
Recognise mathematics equations.
.It Fl -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.
.It Fl -parse-no-autolink
Do not parse
.Li http ,
.Li https ,
.Li ftp ,
.Li mailto ,
and relative links or link fragments.
.It Fl -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.
.It Fl -parse-no-codeindent
Do not parse indented content as code blocks.
.It Fl -parse-no-callouts
Do not parse GFM/MDN callouts
.Pq Qq admonitions .
.It Fl -parse-no-deflists
Do not parse PHP extra definition lists.
.It Fl -parse-no-ext-attrs
Do not parse PHP extra extended attributes.
.It Fl -parse-no-fenced
Do not parse GFM fenced (language-specific) code blocks.
.It Fl -parse-no-footnotes
Do not parse MMD footnotes.
.It Fl -parse-no-img-ext
Deprecated.
See
.Fl -parse-no-ext-attrs .
.It Fl -parse-no-intraemph
Do not parse emphasis within words and links.
.It Fl -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.
.It Fl -parse-no-metadata
Do not parse metadata.
This does not affect metadata given on
.Fl m
or
.Fl M .
.It Fl -parse-no-strike
Do not parse strikethroughs.
.It Fl -parse-no-super
Do not parse super-scripts or sub-scripts at all.
.It Fl -parse-no-tables
Do not parse GFM tables.
.It Fl -parse-no-tasklists
Do not parse GFM task lists.
.It Fl -parse-super-short
If super-script parsing is enabled, use the traditional
non-GFM
.Qq short
syntax.
.El
.Pp
There are many output options.
The following are shared by all output modes:
.Bl -tag -width Ds
.It Fl -out-standalone
Alias for
.Fl s .
.It Fl -out-no-smarty
Do not use the smart typography filter.
By default, certain character sequences are translated into
output-specific glyphs.
.El
.Pp
What follows are per-output options.
For HTML with
.Fl t Ns Ar html ,
these are as follows:
.Bl -tag -width Ds
.It Fl -html-callout-mdn , -html-callout-gfm
Output either or both MDN or GFM callout syntaxes.
.It Fl -html-hardwrap
Hard-wrap paragraph content by outputting line breaks where applicable.
.It Fl -html-no-escapehtml
If
.Fl -html-no-skiphtml
has been specified, this causes embedded HTML not to be escaped, and is
instead output verbatim.
This has no effect if
.Fl -html-no-skiphtml
has not been specified.
.It Fl -html-no-head-ids
Do not output
.Li id
attributes for headers.
.It Fl -html-no-num-ent
Don't normalise HTML entities (when possible) as numeric ones and
instead use the entities as given on input.
.It Fl -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.
.It Fl -html-no-skiphtml
Output embedded HTML.
By default, embedded HTML is not output at all.
See
.Fl -html-no-escapehtml .
.El
.Pp
For both
.Fl t Ns Ar man
and
.Fl t Ns Ar ms ,
the following apply:
.Bl -tag -width Ds
.It Fl -nroff-code-font Ns = Ns Ar fonts
Override the default constant-width fonts with a tuple of regular, bold,
italic, and bold-italic variants in that order.
For example,
.Li B,B,BI,BI
uses bold
.Pq Qq B
instead of a constant-width.
Not specifying a font will use the default, as will specifying a
zero-length font name.
Aliases
.Li none ,
.Li bold ,
and
.Li code
set no special fonts, bold, and the default constant-width.
.It Fl -nroff-no-groff
Don't use
.Xr groff 1
style section headings, PDF hyperlinks and multi-page tables (these further
require
.Fl t Ns Ar ms
mode and
.Fl m Ns Ar spdf
passed to
.Xr groff 1 ) ,
or Unicode sequence syntax.
The output is compatible with traditional
.Xr troff 1 .
.It Fl -nroff-no-numbered
Don't output numbered headings.
Only applies to
.Fl t Ns Ar ms .
.It Fl -nroff-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.
.It Fl -nroff-nolinks
Don't show URLs for images and links (autolinks are still shown).
.Pq Link content is still shown.
Overrides
.Fl -nroff-shortlinks
for images and links.
Applies to
.Fl t Ns Ar man
or when
.Fl nroff-no-groff
is specified.
.It Fl -nroff-shortlinks
Shorten URLs for images, links, and autolinks to only the domain name
and final path.
Applies to
.Fl t Ns Ar man
or when
.Fl nroff-no-groff
is specified.
.El
.Pp
The
.Fl t Ns Ar term
output has the following:
.Bl -tag -width Ds
.It Fl -term-all-metadata
If
.Fl s
is specified, output all metadata instead of just the title, author, and
date.
.It Fl -term-columns=columns
The number of columns in the screen.
Useful for when running in a pipe.
Defaults to what the terminal reports or 72 if in a pipe.
.It Fl -term-hmargin=margin
The number of left margin spaces.
Truncated to the number of columns.
Defaults to zero.
.It Fl -term-no-ansi
Don't show ANSI styles at all.
This implies
.Fl -term-no-colour .
.It Fl -term-no-colour
Don't show ANSI colours.
This will still decorate text with underlines, bolds, and italics, but
not emit any colour codes.
.It Fl -term-nolinks
Don't show URLs for images and links (autolinks are still shown).
.Pq Link content is still shown.
Overrides
.Fl -term-shortlinks
for images and links.
.It Fl -term-shortlinks
Shorten URLs for images, links, and autolinks to only the domain name
and final path.
.It Fl -term-vmargin=margin
The number of top and bottom margin newlines.
Defaults to zero.
.It Fl -term-width=width
Set the soft limit on the number of characters per line.
This may be exceeded by literal text.
The default (or if zero) is the number of terminal columns or 80 at
most.
.El
.Pp
The
.Fl t Ns Ar gemini
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.
.Bl -tag -width Ds
.It Fl -gemini-link-end
Emit the queue of links at the end of the document instead of after the
nearest block element.
.It Fl -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.
.It Fl -gemini-link-noref
Do not format link labels.
Takes precedence over
.Fl -gemini-link-roman .
.It Fl -gemini-link-roman
When formatting link labels, use lower-case Roman numerals instead of the
default lower-case hexavigesimal (i.e.,
.Dq a ,
.Dq b ,
\&...,
.Dq aa ,
.Dq ab ,
\&...).
.It Fl -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.
.El
.Pp
The
.Fl t Ns Ar latex
output has the following options:
.Bl -tag -width Ds
.It Fl -latex-no-numbered
Don't number sections (and subsections, etc.).
.It Fl -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.
.El
.Pp
The
.Fl t Ns Ar fodt
output has the following options:
.Bl -tag -width Ds
.It Fl -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.
.It Fl -odt-style Ns = Ns Ar file
Specify an OpenDocument style file, which must consist of at least
.Li <office:font-face-decls> ,
.Li <office:scripts> ,
and
.Li <office:styles>
XML elements in the root of the document.
This is not syntax-checked in any way.
.El
.Ss Output modes
The output media is specified by
.Fl t ,
which defaults to
.Fl t Ns Ar html .
.Bl -tag -width Ds
.It Fl t Ns Ar fodt
.Dq 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.
Differences are rendered using document tracking.
.It Fl t Ns Ar gemini
Gemini protocol output.
This output mode is experimental.
Differences are not currently rendered.
.It Fl t Ns Ar html
HTML5 output with UTF-8 encoding.
Differences are rendered using the
.Li <ins>
and
.Li <del>
elements.
.It Fl t Ns Ar latex
Simple LaTeX output.
The following packages are required:
.Li amsmath
and
.Li amssymb
for maths,
.Li graphicx
for images,
.Li inputenc Pq utf8
for UTF-8 input,
.Li fontend Pq T1
and
.Li textcomp
for output glyphs,
.Li lmodern
for Latin modern font,
.Li xcolor
for the difference engine output, and
.Li hyperref
for links.
Differences are rendered by colouring in blue (insert) and red (delete)
(this format is not fixed).
.It Fl t Ns Ar man
The
.Ar man
macro package suitable for reading by
.Xr groff 1 ,
.Xr mandoc 1 ,
or traditional
.Xr troff 1 .
Does not support equations and images.
Table support is provided by
.Xr tbl 1 .
Since UTF-8 may be passed as input values,
.Xr preconv 1
may need to be used.
Differences are rendered by colouring in blue (insert) and red (delete)
(this format is not fixed).
.It Fl t Ns Ar ms
The
.Ar ms
macro package suitable for reading by
.Xr groff 1
or traditional
.Xr 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
.Xr tbl 1 .
Since UTF-8 may be passed as input values,
.Xr preconv 1
may need to be used.
Differences are rendered by colouring in blue (insert) and red (delete)
(this format is not fixed).
.It Fl t Ns Ar term
ANSI-escaped UTF-8 output suitable for reading on the terminal.
Images and equations not supported.
Differences are rendered by background-colouring in blue (insert) and
red (delete) (this format is not fixed).
.It Fl t Ns Ar tree
Debugging output: not for general use.
.El
.Ss Standalone documents
When
.Fl s
is specified, additional content may be added to output:
.Bl -tag -width Ds
.It Fl t Ns Ar fodt
Envelope
.Li <office:document>
and prologue
.Li <office:automatic-styles> ,
.Li <office:master-styles> ,
and
.Li <office:body> .
.It Fl t Ns Ar html
Envelope
.Li <html>
and prologue
.Li <head> .
.It Fl t Ns Ar latex
Prologue
.Li documentclass
and
.Li usepackage
statements, and surrounding
.Li begin{document}
statements.
.It Fl t Ns Ar man , Fl t Ns Ar ms
Prologue macros.
.It Fl t Ns Ar term
Prologue lines.
.El
.Pp
If parsed from the document or as given by
.Fl m
or
.Fl M ,
the following metadata keys are used by additional content.
The metadata keys are canonicalised in lowercase and without spaces.
.Pp
Metadata values should not be encoded in their output format, e.g.,
.Dq css: foo&amp;bar .
The renderer will perform any necessary output encoding.
.Bl -tag -width Ds
.It Li affiliation
Author affiliation (organisation or institution).
Multiple affiliations may be separated by two or more spaces (including
newlines).
Used in
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
and
.Fl t Ns Ar ms .
.It Li author
Document author.
Multiple authors may be separated by two or more spaces (including
newlines).
Overridden by
.Li rcsauthor .
Used in
.Fl t Ns Ar fodt ,
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
.Fl t Ns Ar ms ,
and
.Fl t Ns Ar term .
.It Li baseheaderlevel
Added to each header level.
Deprecated in favour of
.Li shiftheadinglevelby .
.It Li copyright
A document copyright (without the word
.Dq Copyright ) ,
for example,
.Dq 2017, Kristaps Dzonsons .
Used in
.Fl t Ns Ar ms
and
.Fl t Ns Ar html .
.It Li css
A CSS file included in the HTML5 document head.
Multiple CSS files (in order) may be separated by two or more spaces
(including newlines).
Only used in
.Fl t Ns Ar html .
.It Li date
Document date in ISO-8601 YYYY-MM-DD format.
Overridden by
.Li rcsdate .
Used in
.Fl t Ns Ar fodt ,
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
.Fl t Ns Ar man ,
.Fl t Ns Ar ms ,
and
.Fl t Ns Ar term .
.It Li javascript
A JavaScript file included in the HTML5 document head.
Multiple script files (in order) may be separated by two or more spaces
(including newlines).
Only used in
.Fl t Ns Ar html .
.It Li lang
Document language in RFC 5646 format.
Only used in
.Fl t Ns Ar html .
.It Li rcsauthor
Like
.Li author ,
but in RCS author format.
Overrides
.Li author .
.It Li rcsdate
Like
.Li date ,
but in RCS date format.
Overrides
.Li date .
.It Li section
Man page section, defaulting to
.Dq 7 .
Only used in
.Fl t Ns Ar man .
.It Li shiftheadinglevelby
Shift all headers by the given number.
For example, a value of 1 causes headers originally at level 1
.Pq Dq <h1>
to be level 2
.Pq Dq <h2> ,
while a value of -1 moves level 2 to 1.
Levels will not move to less than 1.
Takes precedence over
.Li baseheaderlevel .
If unset or not a valid number, defaults to zero.
Used in
.Fl t Ns Ar fodt ,
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
.Fl t Ns Ar man ,
and
.Fl t Ns Ar ms .
.It Li source
Man page source (organisation providing the manual).
Only used in
.Fl t Ns Ar man .
.It Li volume
Man page volume (describes the manual page section).
Only used in
.Fl t Ns Ar man .
.It Li title
Document title.
Used in
.Fl t Ns Ar fodt ,
.Fl t Ns Ar html ,
.Fl t Ns Ar latex ,
.Fl t Ns Ar man ,
.Fl t Ns Ar ms ,
and
.Fl t Ns Ar term .
.El
.Pp
Metadata values are parsed and may be used as variables in markdown
documents regardless of whether
.Fl s
is specified or not.
.Pp
Default values, such
.Dq 7
for the
.Li section ,
are not set as metadata values, and will not appear if the metadata key
is used as a variable.
.Pp
Differences in additional content metadata are rendered differently than
in the document body: deleted metadata key-value pairs are not processed
in the output, so only inserted or retained metadata are processed.
.Pp
In formats where metadata are part of the document body, such as
.Fl t Ns Ar term
and
.Fl t Ns Ar tree ,
all metadata are shown as if in the document body.
.Sh ENVIRONMENT
.Bl -tag -width Ds
.It Ev NO_COLOR
Do not emit colours when in
.Fl t Ns Ar term
mode.
Synonym for
.Ev NO_COLOUR .
Same as
.Fl -term-nocolour .
.El
.Sh FILES
.Bl -tag -width Ds
.It Pa share/odt/styles.xml
Default styles used when generating standalone
.Fl t Ns Ar fodt
documents.
Template for
.Fl -odt-style
styles.
.El
.Sh EXIT STATUS
.Ex -std
.Sh EXAMPLES
To view Markdown differences on an ANSI-compatible, UTF-8 terminal:
.Pp
.Dl lowdown-diff -tterm old.md new.md | less -R
.Pp
The terminal may also be used with
.Xr groff 1
rendering:
.Bd -literal -offset indent
lowdown-diff -stms old.md new.md | \e
  groff -itk -mspdf -Tutf8 | less -R
lowdown-diff -stman old.md new.md | \e
  groff -itk -man -Tutf8 | less -R
.Ed
.Pp
To emit a standalone HTML5 document:
.Pp
.Dl lowdown-diff -s old.md new.md > foo.html
.Pp
To use
.Xr groff 1
to format as a PS file:
.Bd -literal -offset indent
lowdown-diff -stms old.md new.md | \e
  groff -itk -mspdf > foo.ps
.Ed
.Pp
Or with LaTeX:
.Bd -literal -offset indent
lowdown-diff -stlatex old.md new.md > foo.latex
pslatex foo.latex
.Ed
.Pp
PDF generation follows similar logic:
.Bd -literal -offset indent
lowdown-diff -stms old.md new.md | \e
  pdfroff -itk -mspdf > foo.pdf
lowdown-diff -stlatex old.md new.md > foo.latex
pdflatex foo.latex
.Ed
.Pp
UTF-8 support for
.Xr 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
.Pa devpdf
set of the
.Xr groff 1
font directory and are prefixed with
.Sq U .
.Bd -literal -offset indent
lowdown-diff -stms old.md new.md | \e
  pdfroff -itk -mspdf -FU-T > foo.pdf
.Ed
.Sh SEE ALSO
.Xr lowdown 1 ,
.Xr lowdown 3 ,
.Xr lowdown 5
.Sh AUTHORS
.Nm
was written by
.An Kristaps Dzonsons ,
.Mt kristaps@bsd.lv .
.Sh CAVEATS
When viewing
.Fl t Ns Ar man
differences with
.Xr mandoc 1 ,
the marker colours are not rendered.
The
.Fl t Ns Ar gemini
output also currently has no way of encoding differences.