OmegaScript adds processed text-generation commands to text templates (which will usually be HTML, but can be XML or another textual format). Commands take the form $command{comma,separated,arguments} or $simplecommand, for example:


You searched for '$html{$query}'.


Where appropriate, arguments themselves can contain OmegaScript commands. Where an argument is treated as a string, the string is precisely the contents of that argument - there is no string delimiter (such as the double-quote character '"' in C and similar languages). This can make complex OmegaScript slightly difficult to read at times.

When a command takes no arguments, the braces must be omitted (i.e. $msize rather than $msize{} - the latter is a command with a single empty argument). If you want to have the value of $msize immediately followed by a letter, digit, or "_", you can use an empty comment (${}) to prevent the parser treating the following character as part of a command name. E.g. _$msize${}_ rather than _$msize_

It is important to realise that all whitespace is significant in OmegaScript - e.g. if you put whitespace around a "," which separates two command arguments then the whitespace will be part of the respective arguments.

Note that (by design) OmegaScript has no unbounded looping constructs. You can loop over entries in a list, but you can't loop until some arbitrary condition is met. This means that it's not possible to accidentally (or deliberately!) write an OmegaScript template which contains an infinite loop.

OmegaScript literals

$$ - literal '$'
$( - literal '{'
$) - literal '}'
$. - literal ','

OmegaScript commands

In the following descriptions, a LIST is a string of tab-separated values.

commented-out code
add filter term TERM as if it had been passed as a B CGI parameter. You must use $addfilter before any command which requires the query to have been parsed - see $setmap for a list of these commands.
list of all terms indexing the document with docid DOCID - if used without a parameter list, them the docid of the current hit is implicitly used.
lookup the value of a CGI parameter. If the same parameter has multiple values, $cgi will pick one arbitrarily - use $cgilist if you want all the values.
return a list of all values of a CGI parameter
return a list of all the unique CGI parameter names, sorted in ascending order by raw byte values.

return UTF-8 for the given Unicode codepoint, e.g. $chr{127866} should display as a beer mug if the font has a suitable glyph.

Since ASCII is a subset of Unicode, you can also produce control characters, e.g. $chr{13} gives a carriage return character.

To convert a UTF-8 character to a Unicode codepoint, see $ord.

Added in Omega 1.3.4.


number of other documents collapsed into current hit inside $hitlist, which might be used like so:

$if{$ne{$collapsed,0},at least $collapsed hidden results ($value{$cgi{COLLAPSE}})}

return position of first occurrence of STRING1 in STRING2, if present. Else return an empty string. Examples:

$contains{fish,goldfish} gives "4"

$contains{fish,shark} gives ""


encode STRING for use as a field in a CSV file. By default, escaping is done as described in RFC4180, except that we treat any byte value not otherwise mentioned as being 'TEXTDATA' (so %x00-%x09, %x0B-%x0C, %x0E-%x1F, %x7F-%xFF are also permitted there). Examples:

$csv{Safe in CSV!} gives Safe in CSV!

$csv{Not "safe"} gives "Not ""safe"""

$csv{3$. 2$. 1} gives "3, 2, 1"

Some CSV consumers don't follow the RFC, in which case you may need to encode additional values. For this reason, $csv provides an highly conservative alternative mode in which any double quote characters in the string are doubled, and the result always wrapped in double quotes. To select this mode, pass a second non-empty argument. Examples:

$csv{Quote anyway,1} gives "Quote anyway"

$csv{Not "safe",1} gives "Not ""safe"""

Added in Omega 1.3.4.

convert a time_t to strftime FMT (default: YYYY-MM-DD). The conversion is done in timezone UTC.
database name (multiple names are returned separated by "/").
number of documents in the database (if multiple databases are being searched, this gives the total number).
define a macro which can take 0 to 9 arguments. You can call it with $MACRONAME (if it take 0 arguments) or $MACRONAME{ARG1,ARG2,ARG3} is it takes arguments. In value, arguments are available as $1, $2, ... $9. In the current implementation, macros can override OmegaScript commands, but this shouldn't be relied on. It's recommended to use capitalised names for macros to avoid collision with future OmegaScript commands.
"and" or "or" (set from CGI variable DEFAULTOP).

returns a list of docids of any documents with document length zero (such documents probably only contain scanned images, rather than machine readable text, or suggest the input filter isn't working well). If TERM is specified, only consider documents matching TERM, otherwise all documents are considered (so Tapplication/pdf reports all PDF files for which no text was found).

If you're using omindex, note that it skips files with zero size, so these won't get reported here as they aren't present in the database.

lookup variable VAR in the environment.
error message (e.g. if a database wouldn't open, or the query couldn't be parsed, or a Xapian exception has been thrown) or empty if there wasn't an error.

lookup field NAME in document DOCID. If DOCID is omitted then the current hit is used (which only works inside $hitlist).

If multiple instances of field exist the field values are returned tab separated, which means you can pass the results to $map, e.g.:

pretty printed filesize (e.g. 1 byte, 100 bytes, 2.1K, 4.0M, 1.3G). If SIZE is negative, expands to nothing.
serialised version of filter-like settings (currently B, N, DATEVALUE, START, END, SPAN, COLLAPSE, DOCIDORDER, SORT, SORTREVERSE, SORTAFTER, and DEFAULTOP) - set xFILTERS to this so that Omega can detect when the filters have changed and force the first page.

list of all terms in the database with prefix PREFIX, intended to be used to allow drop-down lists and sets of radio buttons to be dynamically generated, e.g.:

$if{$map{$cgilist{B},$eq{$substr{$_,0,1},H}},,SELECTED}> Any
<OPTION VALUE="$html{$_}" $if{$find{$cgilist{B},$html{$_}},SELECTED}>
returns the number of the first entry in LIST which is equal to STRING (starting from 0) or the empty string if no entry matches.
name of current format (as set by CGI parameter``FMT``, or the default)
frequency of a term
html escape string (<>&, etc) and highlight any terms from LIST that appear in TEXT by enclosing them in OPEN and CLOSE. If OPEN is specified, but close is omitted, CLOSE defaults to the appropriate closing tag for OPEN (i.e. with a "/" in front and any parameters removed). If both are omitted, then OPEN is set to: <b style="color:XXXXX;background-color:#YYYYYY"> (where YYYYYY cycles through ffff66 99ff99 99ffff ff66ff ff9999 990000 009900 996600 006699 990099 and XXXXX is black is YYYYYY contains an f, and otherwise white) and CLOSE is </b>.
MSet index of current doc (first document in MSet is 0, so if you want to number the hits 1, 2, 3, ... use $add{$hit,1}).
display hitlist using format FMT.
hits per page (as set by HITSPERPAGE, or the default)
return the hostname from url URL
html escape string (<>&" are escaped to &lt;, etc).
html strip tags from string (<...>, etc).

specify an additional HTTP header to be generated by Omega. For example:


If Content-Type is not specified by the template, it defaults to text/html. Headers must be specified before any other output from the OmegaScript template - any $httpheader{} commands found later in the template will be silently ignored.

document id of current document

encode STRING as a JSON string (not including the enclosing quotes), e.g. $json{The path is "C:\"} gives The path is \"C:\\\"

Added in Omega 1.3.1.


encodes LIST (a string of tab-separated values) as a JSON array, e.g. $jsonarray{$split{a "b" c:\}} gives ["a","\"b\"","c:\\"]

Added in Omega 1.3.1, but buggy until 1.3.4.

MSet index one beyond the end of the current page (so $hit runs from 0 to $sub{$last,1}).
number of last page of hits (may be an underestimate unless $thispage == $lastpage).
number of entries in LIST.

pretty print list. If LIST contains 1, 2, 3, 4 then:

"$list{LIST,$. }" = "1, 2, 3, 4"
"$list{LIST,$. , and }" = "1, 2, 3 and 4"
"$list{LIST,List ,$. ,.}" = "List 1, 2, 3, 4."
"$list{LIST,List ,$. , and ,.}" = "List 1, 2, 3 and 4."

NB $list returns an empty string for an empty list (so the last two forms aren't redundant as it may at first appear).

write to the log file LOGFILE in directory log_dir (set in omega.conf). ENTRY is the OmegaScript for the log entry, and a linefeed is appended. If LOGFILE cannot be opened for writing, nothing is done (and ENTRY isn't evaluated). ENTRY defaults to a format similar to the Common Log Format used by webservers.

Return the tag corresponding to key KEY in the CDB file CDBFILE. If the file doesn't exist, or KEY isn't a key in it, then $lookup expands to nothing. CDB files are compact disk based hashtables. For more information and public domain software which can create CDB files, please visit:

An example of how this might be used is to map top-level domains to country names. Create a CDB file tld_en which maps "fr" to "France", "de" to "Germany", etc and then you can translate a country code to the English country name like so:


If a tld isn't in the CDB (e.g. "com"), this will expand to ".com".

You can take this further and prepare a set of CDBs mapping tld codes to names in other languages - tld_fr for French, tld_de for German. Then if you have the ISO language code in $opt{lang} you can replace tld_en with tld_$or{$opt{lang},en} and automatically translate into the currently set language, or English if no language is set.

return UTF-8 text TEXT converted to lower case.

map a list into the evaluated argument. If LIST is 1, 2 then:

"$map{LIST,x$_ = $_; }" = "x1 = 1;     x2 = 2; "

Note that $map{} returns a list (this is a change from older versions). If the tabs are a problem, use $list{$map{...},} to get rid of them.


peform a regex match using Perl-compatible regular expressions. Returns true if a match is found, else it returns an empty string.

The optional OPTIONS argument can contain zero or more of the letters imsx, which have the same meanings as the corresponding Perl regexp modifiers:

  • i - make the pattern matching case-insensitive
  • m - make ^/$ match after/before embedded newlines
  • s - allows . in the pattern to match a linefeed
  • x - allow whitespace and #-comments in the pattern
estimated number of matches.
return true if $msize is exact (or "" if it is estimated). Exactly equivalent to: $eq{$msizelower,$msizeupper}
lower bound on number of matches.
upper bound on number of matches.
pretty print integer (with thousands separator).
number of seconds since the epoch (suitable for feeding to $date). Whether $now returns the same value for repeated calls in the same Omega search session is unspecified.
lookup an option value (as set by $set).
lookup an option within a map (as set by $setmap).

return codepoint for first character of UTF-8 string. If the argument is an empty string, then an empty string is returned.

For example, $ord{One more time} gives 79.

To convert a Unicode code point into a UTF-8 string, see $chr.

Added in Omega 1.3.4.

converts a number to a 4 byte big-endian binary string

percentage score of current hit (in range 1-100).

You probably don't want to show these percentage scores to end users in new applications - they're not really a percentage of anything meaningful, and research seems to suggest that users don't find numeric scores in search results useful.

convert a term to "user form", as it might be entered in a query. If a matching term was entered in the query, just use that (the first occurrence if a term was generated multiple times from a query). Otherwise term prefixes are converted back to user forms as specified by $setmap{prefix,...} and $setmap{boolprefix,...}.
Prettify URL. This command undoes RFC3986 URL escaping which doesn't affect semantics in practice, in order to make a prettier version of a URL for displaying to the user (rather than in links), but which should still work if copied and pasted.

list of query strings for prefix PREFIX. Any tab characters in the query strings are converted to spaces before adding them to the list (since an OmegaScript list is a string with tabs in).

If PREFIX is omitted or empty, this is built from CGI P variable(s) plus possible added terms from ADD and X.

If PREFIX is non-empty, this is built from CGI P.PREFIX variables.

Note: In Omega < 1.3.3, $query simply joins together the query strings with spaces rather than returning a list.

a human readable description of the Xapian::Query object which omega builds. Mostly useful for debugging omega itself.
list of probabilistic query terms.
return list of values between START and END.
raw record contents of document ID.
document id ID if document is relevant, "" otherwise (side-effect: removes id from list of relevant documents returned by $relevants).
return list of relevant documents
score (0-10) of current hit (equivalent to $div{$percentage,10}).

set option value which may be looked up using $opt. You can use options as variables (for example, to store values you want to reuse without recomputing). There are also several which Omega looks at and which you can set or use:

  • decimal - the decimal separator ("." by default - localised query templates may want to set this to ",").
  • thousand - the thousands separator ("," by default - localised query templates may want to set this to ".", " ", or "").
  • stemmer - which stemming language to use ("english" by default, other values are as understood by Xapian::Stem, so "none" means no stemming).
  • stem_all - if "true", then tell the query parser to stem all words, even capitalised ones.
  • spelling - if "true", then the query parser spelling correction feature is enabled and $suggestion can be used. Deprecated - use flag_spelling_correction instead (which was added in version 1.2.5).
  • fieldnames - if set to a non-empty value then the document data is parsed with each line being the value of a field, and the names are taken from entries in the list in fieldnames. So $set{fieldnames,$split{title sample url}} will take the first line as the "title" field, the second as the "sample" field and the third as the "url" field. Any lines without a corresponding field name will be ignored. If unset or empty then the document data is parsed as one field per line in the format NAME=VALUE (where NAME is assumed not to contain '=').
  • weighting - set the weighting scheme to use, and (optionally) the parameters to use if the weighting scheme supports them. The syntax is a string consisting of the scheme name followed by any parameters, all separated by whitespace. Any parameters not specified will use their default values. Valid scheme names are bb2 (in Omega >= 1.3.2), bm25, bool, coord (in Omega >= 1.4.1), dlh (in Omega >= 1.3.2), dph (in Omega >= 1.3.2), ifb2 (in Omega >= 1.3.2), ineb2 (in Omega >= 1.3.2), inl2 (in Omega >= 1.3.2), lm (in Omega >= 1.3.2), pl2 (in Omega >= 1.3.2), tfidf (in Omega >= 1.3.1), and trad. e.g. $set{weighting,bm25 1 0.8}
  • expansion - set the query expansion scheme to use, and (optionally) the parameters to use if the expansion scheme supports them. The syntax is a string consisting of the scheme name followed by any parameters, all separated by whitespace. Any parameters not specified will use their default values. Valid expansion schemes names are trad and bo1. e.g. $set{expansion,trad 2.0}
  • weightingpurefilter - normally a query consisting only of filter terms won't have relevance weights calculated. This option allows you to specify a weighting scheme to use for such queries, with the same values supported as for weighting above. For example, $set{weightingpurefilter,coord} will weight such queries by how many filter terms match each document.

Omega 1.2.5 and later support the following options, which can be set to a non-empty value to enable the corresponding QueryParser flag. Omega sets flag_default to true by default - you can set it to an empty value to turn it off ($set{flag_default,}):

  • flag_auto_multiword_synonyms
  • flag_auto_synonyms
  • flag_boolean
  • flag_boolean_any_case
  • flag_cjk_ngram (new in 1.2.22 and 1.3.4)
  • flag_default
  • flag_lovehate
  • flag_partial
  • flag_phrase
  • flag_pure_not
  • flag_spelling_correction
  • flag_synonym
  • flag_wildcard

Omega 1.2.7 added support for search fields with a probabilistic prefix, and you can set different QueryParser flags for each prefix - for example, for the XFOO prefix use XFOO:flag_pure_not, etc. The unprefixed constants provide a default value for these. If a flag is set in the default, the prefix specific flag can unset it if it is set to the empty value (e.g. $set{flag_pure_not,1}$set{XFOO:flag_pure_not,}).

You can use :flag_partial, etc to set or unset a flag just for unprefixed fields.

Similarly, XFOO:stemmer specifies the stemmer to use for field XFOO, with stemmer providing a default.

add documents into the RSet

set a map of option values which may be looked up against using $opt{MAP,NAME} (maps with the same name are merged rather than the old map being completely replaced).

You can create and use of maps in your own templates, but Omega also has several standard maps used to control building the query:

Omega uses the "prefix" map to set the prefixes understood by the query parser. So if you wish to translate a prefix of "author:" to A and "title:" to "S" you would use:


In Omega 1.3.0 and later, you can map a prefix in the query string to more than one term prefix by specifying an OmegaScript list, for example to search unprefixed and S prefix by default use this (this also shows how you can map from an empty query string prefix, and also that you can map to an empty term prefix - these don't require Omega 1.3.0, but become much more useful in combination with this new feature):

$setmap{prefix,,$split{ S}}

Similarly, if you want to be able to restrict a search with a boolean filter from the text query (e.g. "group:" to "G") you would use:


Don't be tempted to add whitespace around the commas, unless you want it to be included in the names and values!

Another map (added in Omega 1.3.4) allows specifying any boolean prefixes which are non-exclusive, i.e. multiple filters of that type should be combined with OP_AND rather than OP_OR. For example, if you have have a boolean filter on "material" using the XM` prefix, and the items being searched are made of multiple materials, you likely want multiple material filters to restrict to items matching all the materials (the default it to restrict to any of the materials). To specify this use $setmap{nonexclusiveprefix,XM,true} (any non-empty value can be used in place of true) - this feature affect both filters from B CGI parameters (e.g. B=XMglass&B=XMwood` and those from parsing the query (e.g. material:glass material:wood if $setmap{boolprefix,material,XM} is also in effect).

Note: you must set the prefix-related maps before the query is parsed. This is done as late as possible - the following commands require the query to be parsed: $prettyterm, $query, $querydescription, $queryterms, $relevant, $relevants, $setrelevant, $unstem, and also these commands require the match to be run which requires the query to be parsed: $freqs, $hitlist, $last, $lastpage, $msize, $msizeexact, $terms, $thispage, $time, $topdoc, $topterms.


returns the elements from LIST at the positions listed in the second list POSITIONS. The first item is at position 0. Any positions which are out of range will be ignored.

For example, if LIST contains a, b, c, d then:

"$slice{LIST,2}" = "c"
"$slice{LIST,1 3}" = "b        d"
"$slice{LIST,$range{1,3}}" = "b        c       d"
"$slice{LIST,$range{-10,10}}" = "a     b       c       d"
Generate a context-sensitive snippet from TEXT using Xapian::MSet::snippet(). The snippet will be at most LENGTH bytes long (default: 200).



returns a list by splitting the string STRING into elements at each occurrence of the substring SPLIT. If SPLIT isn't specified, it defaults to a single space. If SPLIT is empty, STRING is split into individual bytes.

For example:

"$split{one two three}" = "one two     three"
returns a list of any terms in the query which were ignored as stopwords.

returns the substring of STRING which starts at byte position START (the start of the string being 0) and is LENGTH bytes long (or to the end of STRING if STRING is less than START``+``LENGTH bytes long). If LENGTH is omitted, the substring from START to the end of STRING is returned.

If START is negative, it counts back from the end of STRING (so $substr{hello,-1} is o).

If LENGTH is negative, it instead specifies the number of bytes to omit from the end of STRING (so "$substr{example,2,-2}" is "amp"). Note that this means that "$substr{STRING,0,N}$substr{STRING,N}" is "STRING" whether N is positive, negative or zero.

if $set{spelling,true} was done before the query was parsed, then $suggestion will return any suggested spelling corrected version of the query string. If there are no spelling corrections, it will return an empty string.
list of query terms matching the current hit. The ability to specify a prefix was added in Omega 1.3.5. If no prefix is specified (i.e. $terms), then only terms from the query string(s) are returned. This is different to an empty prefix (i.e. $terms{}) which returns all query terms matching the current hit, so also includes filter terms.
page number of current page.
how long the match took (in seconds) e.g. 0.078534. If no timing information was available, returns an empty value.
first document on current page of hit list (counting from 0)
list of up to N top relevance feedback terms (default 16)

transform string using Perl-compatible regular expressions. This command is sort of like the Perl code:

my $string = STRING;
$string =~ s/REGEXP/SUBST/;
print $string;

In SUBST, \1 to \9 are substituted by the 1st to 9th bracket grouping (or are empty if there is no such bracket grouping). \\ is a literal backslash.

The optional OPTIONS argument is supported by Omega 1.3.4 and later. It can contain zero or more of the letters gimsx, which have the same meanings as the corresponding Perl regexp modifiers:

  • g - replace all occurrences of the pattern in the string
  • i - make the pattern matching case-insensitive
  • m - make ^/$ match after/before embedded newlines
  • s - allows . in the pattern to match a linefeed
  • x - allow whitespace and #-comments in the pattern

truncate STRING to LEN bytes, but try to break after a word (unless that would mean truncating to much less than LEN). If we have to split a word, then IND is appended (if specified). If we have to truncate (but don't split a word) then IND2 is appended (if specified). For example:

$truncate{$field{text},500,..., ...}
remove duplicates from a sorted list

converts a 4 byte big-endian binary string to a number, for example:

maps a stemmed term to a list of the unstemmed forms of it used in the query
return UTF-8 text TEXT converted to upper case.
url encode argument
returns value number VALUENO for document DOCID. If DOCID is omitted then the current hit is used (which only works inside $hitlist).
omega version string - e.g. "xapian-omega 1.2.6"
raw document weight of the current hit, as a floating point value (mostly useful for debugging purposes).

Numeric Operators:

add arguments together (if called with one argument, this will convert it to a string and back, which ensures it is an integer).
returns int(A / B) (or the text "divide by 0" if B is zero)
returns int(A % B) (or the text "divide by 0" if B is zero)
maximum of the arguments
minimum of the arguments

$mul{A,B,...} multiply arguments together

returns int((A * B) / C) (or the text "divide by 0" if C is zero)
returns (A - B)

Logical Operators:

logical short-cutting "and" of its arguments - evaluates arguments until it finds an empty one (and returns "") or has evaluated them all (returns "true")
returns "true" if A and B are the same, "" otherwise.
returns "true" if A is numerically >= B.
returns "true" if A is numerically > B.
returns "true" if A is numerically <= B.
returns "true" if A is numerically < B.
returns "true" if A and B are not the same, "" if they are.
returns "true" for the empty string, "" otherwise.
logical short-cutting "or" of its arguments - returns first non-empty argument


if COND is non-empty, evaluate THEN, otherwise evaluate else (if present)
include another OmegaScript file