shocco is a quick-and-dirty, literate-programming-style documentation generator written for and in POSIX shell. It borrows liberally from Docco, the original Q&D literate-programming-style doc generator.

shocco(1) reads shell scripts and produces annotated source documentation in HTML format. Comments are formatted with Markdown and presented alongside syntax highlighted code so as to give an annotation effect. This page is the result of running shocco against its own source file.

shocco is built with make(1) and installs under /usr/local by default:

git clone git://
cd shocco
sudo make install
# or just copy 'shocco' wherever you need it

Once installed, the shocco program can be used to generate documentation for a shell script:


The generated HTML is written to stdout.


Usage and Prerequisites

The most important line in any shell program.

set -e

There’s a lot of different ways to do usage messages in shell scripts. This is my favorite: you write the usage message in a comment — typically right after the shebang line — BUT, use a special comment prefix like #/ so that its easy to pull these lines out.

This also illustrates one of shocco’s corner features. Only comment lines padded with a space are considered documentation. A # followed by any other character is considered code.

#/ Usage: shocco [-t <title>] [<source>]
#/ Create literate-programming-style documentation for shell scripts.
#/ The shocco program reads a shell script from <source> and writes
#/ generated documentation in HTML format to stdout. When <source> is
#/ '-' or not specified, shocco reads from stdin.

This is the second part of the usage message technique: grep yourself for the usage message comment prefix and then cut off the first few characters so that everything lines up.

expr -- "$*" : ".*--help" >/dev/null && {
    grep '^#/' <"$0" | cut -c4-
    exit 0

A custom title may be specified with the -t option. We use the filename as the title if none is given.

test "$1" = '-t' && {

Next argument should be the <source> file. Grab it, and use its basename as the title if none was given with the -t option.

: ${title:=$(basename "$file")}

These are replaced with the full paths to real utilities by the configure/make system.


We’re going to need a markdown command to run comments through. This can be Gruber’s (included in the shocco distribution) or Discount’s super fast markdown(1) in C. Try to figure out if either are available and then bail if we can’t find anything.

command -v "$MARKDOWN" >/dev/null || {
    if command -v >/dev/null
    then alias markdown=''
    elif test -f "$(dirname $0)/"
    then alias markdown="perl $(dirname $0)/"
    else echo "$(basename $0): markdown command not found." 1>&2
         exit 1

Check that Pygments is installed for syntax highlighting.

This is a fairly hefty prerequisite. Eventually, I’d like to fallback on a simple non-highlighting preformatter when Pygments isn’t available. For now, just bail out if we can’t find the pygmentize program.

command -v "$PYGMENTIZE" >/dev/null || {
    echo "$(basename $0): pygmentize command not found." 1>&2
    exit 1

Work and Cleanup

Make sure we have a TMPDIR set. The := parameter expansion assigns the value if TMPDIR is unset or null.

: ${TMPDIR:=/tmp}

Create a temporary directory for doing work. Use mktemp(1) if available; but, since mktemp(1) is not POSIX specified, fallback on naive (and insecure) temp dir generation using the program’s basename and pid.

: ${WORK:=$(
      if command -v mktemp 1>/dev/null 2>&1
          mktemp -d "$TMPDIR/$(basename $0).XXXXXXXXXX"
          dir="$TMPDIR/$(basename $0).$$"
          mkdir "$dir"
          echo "$dir"

We want to be absolutely sure we’re not going to do something stupid like use . or / as a work dir. Better safe than sorry.

test -z "$WORK" -o "$WORK" = '/' && {
    echo "$(basename $0): could not create a temp work dir."
    exit 1

We’re about to create a ton of shit under our $WORK directory. Register an EXIT trap that cleans everything up. This guarantees we don’t leave anything hanging around unless we’re killed with a SIGKILL.

trap "rm -rf $WORK" 0


Start out by applying some light preformatting to the <source> file to make the code and doc formatting phases a bit easier. The result of this pipeline is written to a temp file under the $WORK directory so we can take a few passes over it.

Get a pipeline going with the <source> data. We write a single blank line at the end of the file to make sure we have an equal number of code/comment pairs.

(cat "$file" && printf "\n\n# \n\n")         |

We want the shebang line and any code preceding the first comment to appear as the first code block. This inverts the normal flow of things. Usually, we have comment text followed by code; in this case, we have code followed by comment text.

Read the first code and docs headers and flip them so the first docs block comes before the first code block.

    while read -r line

Issue a warning if the first line of the script is not a shebang line. This can screw things up and wreck our attempt at flip-flopping the two headings.

        lineno=$(( $lineno + 1 ))
        test $lineno = 1 && ! expr "$line" : "#!.*" >/dev/null &&
        echo "$(basename $0): $(file):1 [warn] shebang! line missing." 1>&2

Accumulate comment lines into $docsbuf and code lines into $codebuf. Only lines matching /#(?: |$)/ are considered doc lines.

        if expr "$line" : '# ' >/dev/null || test "$line" = "#"
        then docsbuf="$docsbuf$line
        else codebuf="$codebuf$line

If we have stuff in both $docsbuf and $codebuf, it means we’re at some kind of boundary. If $codehead isn’t set, we’re at the first comment/doc line, so store the buffer to $codehead and keep going. If $codehead is set, we’ve crossed into another code block and are ready to output both blocks and then straight pipe everything by exec‘ing cat.

        if test -n "$docsbuf" -a -n "$codebuf"
            if test -n "$codehead"
            then docshead="$docsbuf"
                 printf "%s" "$docshead"
                 printf "%s" "$codehead"
                 echo "$line"
                 exec cat
            else codehead="$codebuf"

We made it to the end of the file without a single comment line, or there was only a single comment block ending the file. Output our docsbuf or a fake comment and then the codebuf or codehead.

    echo "${docsbuf:-#}"
    echo "${codebuf:-"$codehead"}"
)                                            |

Remove comment leader text from all comment lines. Then prefix all comment lines with “DOCS” and interpreted / code lines with “CODE”. The stream text might look like this after moving through the sed filters:

CODE #!/bin/sh
CODE #/ Usage: shocco <file>
DOCS Docco for and in POSIX shell.
CODE PATH="/bin:/usr/bin"
DOCS Start by numbering all lines in the input file...

Once we pass through sed, save this off in our work directory so we can take a few passes over it.

sed -n '
    s/^: \{0,\}# /DOCS /p
    s/^: \{0,\}#$/DOCS /p
    s/^:/CODE /p
' > "$WORK/raw"

Now that we’ve read and formatted our input file for further parsing, change into the work directory. The program will finish up in there.

cd "$WORK"

First Pass: Comment Formatting

Start a pipeline going on our preformatted input. Replace all CODE lines with entirely blank lines. We’re not interested in code right now, other than knowing where comments end and code begins and code begins and comments end.

sed 's/^CODE.*//' < raw                      |

Now squeeze multiple blank lines into a single blank line.

TODO: cat -s is not POSIX and doesn’t squeeze lines on BSD. Use the sed line squeezing code mentioned in the POSIX cat(1) manual page instead.

cat -s                                       |

At this point in the pipeline, our stream text looks something like this:

DOCS Now that we've read and formatted ...
DOCS change into the work directory. The rest ...
DOCS in there.

DOCS First Pass: Comment Formatting
DOCS ------------------------------

Blank lines represent code segments. We want to replace all blank lines with a dividing marker and remove the “DOCS” prefix from docs lines.

sed '
    s/^$/##### DIVIDER/
    s/^DOCS //'                              |

The current stream text is suitable for input to markdown(1). It takes our doc text with embedded DIVIDERs and outputs HTML.

$MARKDOWN                                    |

Now this where shit starts to get a little crazy. We use csplit(1) to split the HTML into a bunch of individual files. The files are named as docs0000, docs0001, docs0002, … Each file includes a single doc section. These files will sit here while we take a similar pass over the source code.

    csplit -sk                               \
           -f docs                           \
           -n 4                              \
           - '/<h5>DIVIDER<\/h5>/' '{9999}'  \
           2>/dev/null                      ||

Second Pass: Code Formatting

This is exactly like the first pass but we’re focusing on code instead of comments. We use the same basic technique to separate the two and isolate the code blocks.

Get another pipeline going on our performatted input file. Replace DOCS lines with blank lines.

sed 's/^DOCS.*//' < raw                     |

Squeeze multiple blank lines into a single blank line.

cat -s                                      |

Replace blank lines with a DIVIDER marker and remove prefix from CODE lines.

sed '
    s/^$/# DIVIDER/
    s/^CODE //'                             |

Now pass the code through pygmentize for syntax highlighting. We tell it the the input is sh and that we want HTML output.

$PYGMENTIZE -l sh -f html                   |

Post filter the pygments output to remove partial <pre> blocks. We add these back in at each section when we build the output document.

sed '
    s/<div class="highlight"><pre>//
    s/^<\/pre><\/div>//'                    |

Again with the csplit(1). Each code section is written to a separate file, this time with a codeXXX prefix. There should be the same number of codeXXX files as there are docsXXX files.

    DIVIDER='/<span class="c"># DIVIDER</span>/'
    csplit -sk                   \
           -f code               \
           -n 4 -                \
           "$DIVIDER" '{9999}'   \
           2>/dev/null ||

At this point, we have separate files for each docs section and separate files for each code section.

HTML Template

Create a function for apply the standard Docco HTML layout, using jashkenas’s gorgeous CSS for styles. Wrapping the layout in a function lets us apply it elsewhere simply by piping in a body.

layout () {
    cat <<HTML
<!DOCTYPE html>
    <meta http-eqiv='content-type' content='text/html;charset=utf-8'>
    <link rel=stylesheet href="">
<div id=container>
    <div id=background></div>
    <table cellspacing=0 cellpadding=0>
        <th class=docs><h1>$1</h1></th>
        <th class=code></th>
        <tr><td class='docs'>$(cat)</td><td class='code'></td></tr>


Alright, we have separate files for each docs section and separate files for each code section. We’ve defined a function to wrap the results in the standard layout. All that’s left to do now is put everything back together.

Start the pipeline with a simple list of split out temp filename. One file per line.

ls -1 docs[0-9]* code[0-9]* 2>/dev/null      |

Now sort the list of files by the number first and then by the type. The list will look something like this when sort(1) is done with it:

sort -n -k1.5 -k1.1r                         |

And if we pass those files to cat(1) in that order, it concatenates them in exactly the way we need. xargs(1) reads from stdin and passes each line of input as a separate argument to the program given.

We could also have written this as:

cat $(ls -1 docs* code* | sort -n -k1.5 -k1.1r)

I like to keep things to a simple flat pipeline when possible, hence the xargs approach.

xargs cat                                    |

Run a quick substitution on the embedded dividers to turn them into table rows and cells. This also wraps each code block in a <div class=highlight> so that the CSS kicks in properly.

    DOCSREPLACE='</pre></div></td></tr><tr><td class=docs>'
    CODEDIVIDER='<span class="c"># DIVIDER</span>'
    CODEREPLACE='</td><td class=code><div class=highlight><pre>'
    sed "
}                                            |

Pipe our recombined HTML into the layout and let it write the result to stdout.

layout "$title"


shocco is the third tool in a growing family of quick-and-dirty, literate-programming-style documentation generators:

  • Docco – The original. Written in CoffeeScript and generates documentation for CoffeeScript, JavaScript, and Ruby.
  • Rocco – A port of Docco to Ruby.

If you like this sort of thing, you may also find interesting Knuth’s massive body of work on literate programming:

Copyright © Ryan Tomayko <>
This is Free Software distributed under the MIT license.