- SEE ALSO
olson - query the Olson timezone database
olson list <criterion>... <attribute>... olson version
This program provides facilities for extracting information from the Olson timezone database. It can be used to assist selection of a timezone, and for other purposes.
The major action to perform is determined by a subcommand, specified as the first command-line argument. The subcommands are:
Searches the Olson database for combinations of entities (mainly timezones) matching specified criteria, and report specified attributes of them. For details see "LISTING" below.
Indicates which version is being used of the Olson database and of the relevant Perl modules. This information is vital in any bug report.
The listing mode searches through the timezones and country-based selection data of the Olson database. Various attributes of the timezones and other entities can be addressed. An attribute can be used in a criterion to determine which items will be displayed, displayed in the output, or used to sort the output. Each command-line argument specifies either a matching criterion, an attribute to display, or a sorting directive. The three kinds of argument can be mixed arbitrarily. At least one attribute to display must be specified, but matching criteria and sorting directives are entirely optional.
The addressable attributes each have a long descriptive name and a short name to save typing. In compound attribute names, segments can be separated with spaces. The attributes are:
Hierarchical name of a timezone, such as "Europe/London". The timezone may be either a canonical timezone or an alias for (link to) a canonical timezone. On input, a timezone name must be supplied with exact casing, and only names of defined timezones will be accepted.
First segment of a geographical timezone name. This is the name of a continent or ocean, and is used for rough geographical categorisation of timezones. There are also timezone names that don't begin with an area name, either because it's not a geographical timezone or because it's a historical alias. On output, an area name has standard capitalisation. On input, an area name is accepted case insensitively, and only names of defined areas will be accepted.
ISO 3166 alpha-2 code of a country. Countries are not used as a primary means of categorising timezones, but country-based categorisation data is supplied to support the selection of timezones based on political geography. On output, a country code is expressed in uppercase. On input, a country code is accepted case insensitively, and only defined country codes will be accepted.
An English name for a country, possibly in a modified form, optimised to help humans find the right entry in alphabetical lists. This is not necessarily identical to the country's standard short or long name.
A brief English description of a segment of a country, used to distinguish between the regions of a single country. Empty string if the country has only one region for timezone purposes.
Hierarchical name of a canonical timezone, such as "Europe/London". On input, a timezone name must be supplied with exact casing, and only names of defined canonical timezones will be accepted.
- offset @ absolute-time
- o @ absolute-time
The offset from UT that a timezone observes at the specified absolute time. See below for the format in which the absolute time must be stated. An offset is expressed in hours, minutes, and seconds, two digits of each, with a leading sign. On output, components are separated by colons, and trailing zero-valued components are omitted. On input, colon separators are optional, and trailing zero-valued components are optional.
- initialism @ absolute-time
- i @ absolute-time
The initialism used to refer to a timezone at the specified absolute time. See below for the format in which the absolute time must be stated. On input, an initialism must be supplied with exact casing.
- dst_status @ absolute-time
- d @ absolute-time
Whether a timezone is observing DST at the specified absolute time. See below for the format in which the absolute time must be stated. It is expressed as a single character: a "
+" indicates DST, and a "
-" indicates not DST.
- local_time @ absolute-time
- t @ absolute-time
The local time in a timezone at the specified absolute time. See below for the format in which the absolute time must be stated. A local time is expressed in the Gregorian calendar in ISO 8601 format: year, month, day, hour, minute, and second. The year is four digits, and the other components two digits. On output, date is separated from time of day by a "T", dash and colon separators are used between components, and all components are emitted. On input, the separators are optional, "T" is accepted case insensitively and can be surrounded or replaced with spaces, and trailing components with the lowest possible value are optional.
Where an absolute time must be used to parameterise an attribute, it can be expressed in these forms:
- local-time Z
Time in UT expressed in ISO 8601 format. The local-time is as described for the local_time attribute, and "Z" indicates that it is UT. "Z" is accepted case insensitively and can be preceded by spaces.
The time at which the program is running. A single time is used as "now" for the entire program run, even if it takes a non-negligible amount of time to run.
Sometimes a proper value for an attribute is not available. On output, this doesn't prevent a line appearing, and the place of the attribute is taken by a possibly-repeated punctuation character signalling the kind of exception. The kinds of exception are:
A particular local time doesn't exist because it is skipped as a timezone changes offset. Typically occurs at Spring DST changes. (Currently this program doesn't support any queries that can generate this exception.)
The information in the Olson database is incomplete. Typically occurs for the distant future in timezones with tricky DST rules.
There is definitively no applicable value. Occurs where entities don't match up at all, for example when requesting the area of a non-geographical timezone. Also occurs when requesting observance data (such as offset) for a disused timezone (e.g., before the location was inhabited).
Criteria restricting which items should be displayed are supplied in command-line arguments. In the criterion syntax, tokens may generally be separated with spaces. Be sure to quote appropriately for your shell, where the operators include shell metacharacters or if using spaces. The forms of criterion are:
- attribute compare value
Compares the value of an attribute against a literal value. Matches if the comparison produces the kind of result requested by the comparison operator. The comparison operators are:
does not sort before
sorts before or equal
does not sort before or equal
does not sort after
sorts after or equal
does not sort after or equal
The positive comparisons never match when the attribute has an exception rather than a normal value, whereas the negative comparisons always match on exception. That is, exceptions don't sort relative to normal values for matching purposes. This is the difference between !< and >=, and the other pairs that otherwise seem equivalent. Normal values always have a defined total ordering.
- attribute ?
Match if the attribute has a normal (non-exception) value.
- attribute !?
Match if the attribute has an exception value.
A command-line argument requesting that an attribute be displayed consists only of the attribute name. A command-line argument controlling sorting consists of the name of an attribute to sort on, preceded by a "+" for standard sorting or "-" for reversed sorting. (Spaces are permitted between the sign and the attribute name.) Items are sorted first according to the supplied sorting directives, first supplied being the most significant. Where the sorting directives don't distinguish items, they are sorted according to the attributes being displayed.
Each line of output describes one combination of entities matching all the specified criteria. Within each line, the values of the attributes requested for display are stated in the order requested, separated by spaces. Most attribute values are expressed without using spaces internally, so splitting the line on spaces suffices to separate the attributes. Watch out for the abnormal `initialism' used by the "Factory" timezone, which, unlike all real initialisms, has internal spaces. Spacing is varied so that in most cases each attribute is a visually distinct column, but wide values will break the column format for a particular line.
Where multiple matching combinations of entities are identical in all the attributes selected for display and sorting, they are merged into one line. As a result, if all the sorting is on attributes being displayed, all the output lines are necessarily different. (Sorting on attributes that are algebraically distant from all those being displayed can result in many identical output lines, which looks strange. The ability to do this may be curtailed in the future.) Any item where all the display and sort attributes have only !!! exceptions (unmatched entities) is suppressed.
Most attribute values are intended to be parseable by computer programs, and therefore the notation is intended to be very stable. The amount of spacing used, however, should not be relied upon.
Entities and relationships
The listing facility can be well understood in terms of the relational algebra commonly seen in databases with SQL. The relevant entity types and their relatioships are:
A named context in which there is an agreed set of behaviour for local clocks. A timezone is primarily identified by its hierarchical name.
A timezone is related to zero or one area, as determined by its name. It is also related to zero or more regions; currently this is never more than one region, but there's no rule requiring such a limit. Via regions, a timezone is related to zero or more (in practice zero or one) countries.
A timezone is related to exactly one canonical timezone, which is what defines the behaviour of local clocks. The algebra is slightly muddled here, because the Olson database uses the same namespace for clock contexts (timezones) and clock behaviour (canonical timezones). In Olson terminology, a timezone is related to a canonical timezone either by being the canonical timezone (if it has behaviour defined in its own right) or by being a link to the canonical timezone.
A broad geographical area, either a continent or an ocean. An area is primarily identified by its monomial name.
An area is related to one or more timezones. This relationship is determined by the timezone's name, of which the area (if any) is the first segment. Via timezones, an area is related to zero or more regions, zero or more countries, and one or more canonical timezones.
A political entity claiming authority over some geographical area. The existence and geographical extent of countries is relatively volatile, and in places controversial, which is why the Olson database doesn't use countries as a primary means to identify timezones. A country is primarily identified by its ISO 3166 alpha-2 code, and it is this assignment by the ISO 3166 Maintenance Agency that determines what is a country, for the purposes of the Olson database. A country also has a name. Formal country names vary between languages and are often rather long; the Olson database maintains only a short English name for each country.
A country is related to zero or more (in practice always one or more) regions. Via regions, it is related to zero or more (in practice always one or more) timezones, zero or more (in practice always one or more) canonical timezones, and zero or more (in practice always one or more, more being rare) areas.
A geographical segment of a country. It has no primary identifier.
A region has, in the Olson database, a description distinguishing it from other regions of the same country. A region also has a pointlike principal geographical location, identified by latitude and longitude, which is not currently accessible through this program.
A region is related to exactly one country and exactly one timezone. Via the timezone it is related to zero or one area and exactly one canonical timezone.
- canonical timezone
A set of behaviour for local clocks. A canonical timezone is primarily identified by its hierarchical name.
For each absolute time, a canonical timezone has either zero or one combination of offset, initialism, and DST status. These features are treated in this program as attributes, parameterised by absolute time, but in relational algebra would be more properly treated as a relationship to "observance" entities. It is intended that a future version of this program will be able to search among observances within a canonical timezone, treating observances as first-class entities.
A canonical timezone is related to one or more timezone, which is what defines where the clock behaviour is used. See the notes in the timezone entry above about the namespace confusion. Via the timezones, a canonical timezone is related to zero or more areas, zero or more regions, and zero or more countries.
In relational algebra terms, the listing facility selects from a join between all of these entity types. With only distinct result rows being shown, some of the entity types are typically irrelevant, and can be seen as being implicitly dropped from the join. The join is fully outer, meaning that all of the underlying entities are available for output even where they don't relate to any other entities through the join. (This is part of what the exceptions are about.)
List countries in a particular area, as an intermediate step in a user selecting a timezone:
olson list a=pacific c cn +cn
List timezones in a particular country, as the final step in a user selecting a timezone:
olson list c=ki z rd +rd
Which offsets from UT could be meant by "CST"?
olson list i@now=CST o@now
This misses out on any timezones where "CST" is used in part of the year but not right now.
Which timezones have jumped westward across the International Date Line since 1900?
olson list 'o@1900z < -08' 'o@now > +08' k
Andrew Main (Zefram) <email@example.com>
Copyright (C) 2012 Andrew Main (Zefram) <firstname.lastname@example.org>
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.