How to Index Anything

The first step in building an index with SWISH-E is writing a configuration file. Create a directory like ~/indices, cd into it and create the file ./howto-html.conf with the following contents:

# howto-html.conf
IndexDir  ../HOWTO-htmls/
IndexOnly .html
IndexFile ./howto-html.index

The IndexDir directive specifies the directory in which SWISH-E should look for files to be indexed. The IndexOnly directive requests that only files ending in .html be indexed. Finally, the location of the index to be created is specified with the IndexFile directive.

Now, let's build our index of HTML files with the command:

% swish-e -c howto-html.conf

The -c option specifies which SWISH-E configuration file to use. On an older system, building this index may take a few minutes or so; on a contemporary one, it should take under a minute. Figure 1 illustrates the process of indexing HTML files on the filesystem with SWISH-E.

Figure 1. Indexing HTML on the Filesystem with SWISH-E

Let's test our first index by doing a simple search for HTML files relevant to the term NFS. You can test SWISH-E indices quickly using the swish-e executable by specifying an index with the -f option, and the text to be searched with the -w option; searches on SWISH-E indices are case-insensitive. Because we expect a lot of pages (or hits) to include the word NFS, we use the -m 3 option to request only three:

% swish-e -f howto-html.index -m 3 -w nfs

This returns (abridged and reformatted):

1000 ../HOWTO-htmls/NFS-HOWTO/performance.html
        "Optimizing NFS Performance" 33288
998 ../HOWTO-htmls/NFS-HOWTO/intro.html
       "Introduction" 10966
993 ../HOWTO-htmls/NFS-HOWTO/security.html
       "Security and NFS" 35968

Not bad—those pages are definitely about NFS, and the output is intuitive. The first column is the rank SWISH-E gives each hit—the hits considered most relevant always are ranked 1000, with less-relevant files ranked in descending order. The second column shows the name of the file, the third gives the page's title and the fourth shows the byte count of the indexed data. SWISH-E determines the title of each page from the HTML tags in each file using one of its HTML parsing engines.

The built-in SWISH-E parsing engines are called TXT, HTML and XML, and each is designed to parse the corresponding type of content. Recent versions of SWISH-E also can use the libxml2 library for the HTML2 and XML2 parsing back ends. Both the XML2 and HTML2 parsers are preferable to their built-in counterparts—especially HTML2. This is why a recent version of libxml2, though technically optional when building SWISH-E, probably should be considered a prerequisite.

SWISH-E supports a full-featured text retrieval search language with syntax including AND, OR, NOT and parenthetic grouping that all work predictably. For example, the following searches all have the expected semantics:

% swish-e -f howto-html.index -w nfs AND tcp
% swish-e -f howto-html.index -w nfs OR tcp
% swish-e -f howto-html.index \
        -w '(gandalf OR frodo) OR (lord AND rings)'

SWISH-E configuration files are simple text files in which each line is either a directive or a comment. Any line in which the first non-whitespace character is a # is ignored by SWISH-E as a comment. All other non-empty lines should be in the form:

Directive Options [Options] ...

If you need to specify an option with spaces embedded, you can use quotation marks:

Directive "Option With Spaces!"

If the option has single quotation marks within it, you can quote it with the double quote character and vice versa, for example:

Directive "Fred's Index Option"
Directive 'By Josh "joshr" Rabinowitz'

Dozens of directives can be applied to SWISH-E configuration files. An exhaustive reference can be found in the SWISH-E documentation.

Each SWISH-E index is stored in a pair of files. One is named as specified in the IndexFile directive, and the other is called indexname.prop. When talking about a SWISH-E index, we mean this pair of files.

The indices can get large. In our example index of HTML files, the index occupies about 11MB, about one-fourth the size of the original files indexed.