215 lines
8.0 KiB
Plaintext
215 lines
8.0 KiB
Plaintext
What is this?
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=============
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This is an implementation of John Gruber's [markdown][] in C. It uses a
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[parsing expression grammar (PEG)][] to define the syntax. This should
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allow easy modification and extension. It currently supports output in
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HTML, LaTeX, or groff_mm formats, and adding new formats is relatively
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easy.
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[parsing expression grammar (PEG)]: http://en.wikipedia.org/wiki/Parsing_expression_grammar
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[markdown]: http://daringfireball.net/projects/markdown/
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It is pretty fast. A 179K text file that takes 5.7 seconds for
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Markdown.pl (v. 1.0.1) to parse takes less than 0.2 seconds for this
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markdown. It does, however, use a lot of memory (up to 4M of heap space
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while parsing the 179K file, and up to 80K for a 4K file). (Note that
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the memory leaks in earlier versions of this program have now been
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plugged.)
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Both a library and a standalone program are provided.
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peg-markdown is written and maintained by John MacFarlane (jgm on
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github), with significant contributions by Ryan Tomayko (rtomayko).
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It is released under both the GPL and the MIT license; see LICENSE for
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details.
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Installing
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==========
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On a linux or unix-based system
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-------------------------------
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This program is written in portable ANSI C. It requires
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[glib2](http://www.gtk.org/download.html). Most *nix systems will have
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this installed already. The build system requires GNU make.
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The other required dependency, [Ian Piumarta's peg/leg PEG parser
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generator](http://piumarta.com/software/peg/), is included in the source
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directory. It will be built automatically. (However, it is not as portable
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as peg-markdown itself, and seems to require gcc.)
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To make the 'markdown' executable:
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make
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(Or, on some systems, `gmake`.) Then, for usage instructions:
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./markdown --help
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To run John Gruber's Markdown 1.0.3 test suite:
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make test
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The test suite will fail on one of the list tests. Here's why.
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Markdown.pl encloses "item one" in the following list in `<p>` tags:
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1. item one
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* subitem
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* subitem
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2. item two
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3. item three
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peg-markdown does not enclose "item one" in `<p>` tags unless it has a
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following blank line. This is consistent with the official markdown
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syntax description, and lets the author of the document choose whether
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`<p>` tags are desired.
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Cross-compiling for Windows with MinGW on a linux box
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-----------------------------------------------------
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Prerequisites:
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* Linux system with MinGW cross compiler For Ubuntu:
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sudo apt-get install mingw32
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* [Windows glib-2.0 binary & development files](http://www.gtk.org/download-windows.html).
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Unzip files into cross-compiler directory tree (e.g., `/usr/i586-mingw32msvc`).
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Steps:
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1. Create the markdown parser using Linux-compiled `leg` from peg-0.1.4:
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./peg-0.1.4/leg markdown_parser.leg >markdown_parser.c
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(Note: The same thing could be accomplished by cross-compiling leg,
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executing it on Windows, and copying the resulting C file to the Linux
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cross-compiler host.)
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2. Run the cross compiler with include flag for the Windows glib-2.0 headers:
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for example,
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/usr/bin/i586-mingw32msvc-cc -c \
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-I/usr/i586-mingw32msvc/include/glib-2.0 \
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-I/usr/i586-mingw32msvc/lib/glib-2.0/include -Wall -O3 -ansi markdown*.c
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3. Link against Windows glib-2.0 headers: for example,
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/usr/bin/i586-mingw32msvc-cc markdown*.o \
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-Wl,-L/usr/i586-mingw32msvc/lib/glib,--dy,--warn-unresolved-symbols,-lglib-2.0 \
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-o markdown.exe
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The resulting executable depends on the glib dll file, so be sure to
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load the glib binary on the Windows host.
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Compiling with MinGW on Windows
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-------------------------------
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These directions assume that MinGW is installed in `c:\MinGW` and glib-2.0
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is installed in the MinGW directory hierarchy (with the mingw bin directory
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in the system path).
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Unzip peg-markdown in a temp directory. From the directory with the
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peg-markdown source, execute:
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cd peg-0.1.4
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for %i in (*.c) do @gcc -g -Wall -O3 -DNDEBUG -c -o %~ni.o %i
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gcc -o leg.exe leg.o tree.o compile.o
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cd ..
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peg-0.1.4\leg.exe markdown_parser.leg >markdown_parser.c
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@for %i in (markdown*.c) do @gcc -mms-bitfields -Ic:/MinGW/include/glib-2.0 -Ic:/MinGW/lib/glib-2.0/include -c -o %~ni.o %i
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gcc -O3 -Lc:/MinGW/lib/glib-2.0 -lglib-2.0 -lintl markdown.o markdown_lib.o markdown_output.o markdown_parser.o -o markdown.exe -Wl,--dy,--warn-unresolved-symbols,-lglib-2.0,-Lc:/MinGW/lib/glib-2.0,-lglib-2.0,-lintl
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(Windows instructions courtesy of Matt Wolf.)
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Extensions
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==========
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peg-markdown supports extensions to standard markdown syntax.
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These can be turned on using the command line flag `-x` or
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`--extensions`. `-x` by itself turns on all extensions. Extensions
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can also be turned on selectively, using individual command-line
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options. To see the available extensions:
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./markdown --help-extensions
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The `--smart` extension provides "smart quotes", dashes, and ellipses.
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The `--notes` extension provides a footnote syntax like that of
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Pandoc or PHP Markdown Extra.
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Using the library
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=================
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The library exports two functions:
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GString * markdown_to_g_string(char *text, int extensions, int output_format);
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char * markdown_to_string(char *text, int extensions, int output_format);
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The only difference between these is that `markdown_to_g_string` returns a
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`GString` (glib's automatically resizable string), while `markdown_to_string`
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returns a regular character pointer. The memory allocated for these must be
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freed by the calling program, using `g_string_free()` or `free()`.
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`text` is the markdown-formatted text to be converted. Note that tabs will
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be converted to spaces, using a four-space tab stop. Character encodings are
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ignored.
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`extensions` is a bit-field specifying which syntax extensions should be used.
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If `extensions` is 0, no extensions will be used. If it is `0xFFFFFF`,
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all extensions will be used. To set extensions selectively, use the
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bitwise `&` operator and the following constants:
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- `EXT_SMART` turns on smart quotes, dashes, and ellipses.
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- `EXT_NOTES` turns on footnote syntax. [Pandoc's footnote syntax][] is used here.
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- `EXT_FILTER_HTML` filters out raw HTML (except for styles).
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- `EXT_FILTER_STYLES` filters out styles in HTML.
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[Pandoc's footnote syntax]: http://johnmacfarlane.net/pandoc/README.html#footnotes
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`output_format` is either `HTML_FORMAT`, `LATEX_FORMAT`, or `GROFF_MM_FORMAT`.
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To use the library, include `markdown_lib.h`. See `markdown.c` for an example.
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Hacking
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=======
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It should be pretty easy to modify the program to produce other formats
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than HTML or LaTeX, and to parse syntax extensions. A quick guide:
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* `markdown_parser.leg` contains the grammar itself.
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* `markdown_output.c` contains functions for printing the `Element`
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structure in various output formats.
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* To add an output format, add the format to `markdown_formats` in
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`markdown_lib.h`. Then modify `print_element` in `markdown_output.c`,
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and add functions `print_XXXX_string`, `print_XXXX_element`, and
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`print_XXXX_element_list`. Also add an option in the main program
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that selects the new format. Don't forget to add it to the list of
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formats in the usage message.
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* To add syntax extensions, define them in the PEG grammar
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(`markdown_parser.leg`), using existing extensions as a guide. New
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inline elements will need to be added to `Inline =`; new block
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elements will need to be added to `Block =`. (Note: the order
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of the alternatives does matter in PEG grammars.)
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* If you need to add new types of elements, modify the `keys`
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enum in `markdown_peg.h`.
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* By using `&{ }` rules one can selectively disable extensions
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depending on command-line options. For example,
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`&{ extension(EXT_SMART) }` succeeds only if the `EXT_SMART` bit
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of the global `syntax_extensions` is set. Add your option to
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`markdown_extensions` in `markdown_lib.h`, and add an option in
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`markdown.c` to turn on your extension.
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* Note: Avoid using `[^abc]` character classes in the grammar, because
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they cause problems with non-ascii input. Instead, use: `( !'a' !'b'
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!'c' . )`
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