diff options
Diffstat (limited to 'zic.8.txt')
| -rw-r--r-- | zic.8.txt | 145 |
1 files changed, 74 insertions, 71 deletions
diff --git a/zic.8.txt b/zic.8.txt index acef001bbafd..c72f8512548d 100644 --- a/zic.8.txt +++ b/zic.8.txt @@ -77,16 +77,16 @@ OPTIONS due to the need to represent the timestamp range boundaries, particularly if hi causes a TZif file to contain explicit entries for pre-hi transitions rather than concisely - representing them with an extended POSIX.1-2017 TZ string. Also - see the -b slim option for another way to shrink output size. + representing them with a proleptic TZ string. Also see the -b + slim option for another way to shrink output size. - -R @hi Generate redundant trailing explicit transitions for timestamps + -R @hi Generate redundant trailing explicit transitions for timestamps that occur less than hi seconds since the Epoch, even though the - transitions could be more concisely represented via the extended - POSIX.1-2017 TZ string. This option does not affect the + transitions could be more concisely represented via the + proleptic TZ string. This option does not affect the represented timestamps. Although it accommodates nonstandard - TZif readers that ignore the extended POSIX.1-2017 TZ string, it - increases the size of the altered output files. + TZif readers that ignore the proleptic TZ string, it increases + the size of the altered output files. -t file When creating local time information, put the configuration link @@ -97,34 +97,33 @@ OPTIONS The input specifies a link to a link, something not supported by some older parsers, including zic itself through release 2022e. - A year that appears in a data file is outside the range of + A year that appears in a data file is outside the range of representable years. A time of 24:00 or more appears in the input. Pre-1998 versions - of zic prohibit 24:00, and pre-2007 versions prohibit times + of zic prohibit 24:00, and pre-2007 versions prohibit times greater than 24:00. - A rule goes past the start or end of the month. Pre-2004 + A rule goes past the start or end of the month. Pre-2004 versions of zic prohibit this. A time zone abbreviation uses a %z format. Pre-2015 versions of zic do not support this. - A timestamp contains fractional seconds. Pre-2018 versions of + A timestamp contains fractional seconds. Pre-2018 versions of zic do not support this. The input contains abbreviations that are mishandled by pre-2018 - versions of zic due to a longstanding coding bug. These - abbreviations include "L" for "Link", "mi" for "min", "Sa" for + versions of zic due to a longstanding coding bug. These + abbreviations include "L" for "Link", "mi" for "min", "Sa" for "Sat", and "Su" for "Sun". - The output file does not contain all the information about the - long-term future of a timezone, because the future cannot be - summarized as an extended POSIX.1-2017 TZ string. For example, - as of 2023 this problem occurs for Morocco's daylight-saving - rules, as these rules are based on predictions for when Ramadan - will be observed, something that an extended POSIX.1-2017 TZ - string cannot represent. + The output file does not contain all the information about the + long-term future of a timezone, because the future cannot be + summarized as a proleptic TZ string. For example, as of 2023 + this problem occurs for Morocco's daylight-saving rules, as + these rules are based on predictions for when Ramadan will be + observed, something that a proleptic TZ string cannot represent. The output contains data that may not be handled properly by client code designed for older zic output formats. These @@ -309,24 +308,28 @@ FILES RULES The name of the rules that apply in the timezone or, alternatively, a field in the same format as a rule-line SAVE - column, giving the amount of time to be added to local standard + field, giving the amount of time to be added to local standard time and whether the resulting time is standard or daylight - saving. If this field is - then standard time always applies. - When an amount of time is given, only the sum of standard time - and this amount matters. - - FORMAT The format for time zone abbreviations. The pair of characters - %s is used to show where the "variable part" of the time zone - abbreviation goes. Alternatively, a format can use the pair of - characters %z to stand for the UT offset in the form +-hh, - +-hhmm, or +-hhmmss, using the shortest form that does not lose - information, where hh, mm, and ss are the hours, minutes, and - seconds east (+) or west (-) of UT. Alternatively, a slash (/) - separates standard and daylight abbreviations. To conform to - POSIX, a time zone abbreviation should contain only alphanumeric - ASCII characters, "+" and "-". By convention, the time zone - abbreviation "-00" is a placeholder that means local time is - unspecified. + saving. Standard time applies if this field is - or for + timestamps occurring before any rule takes effect. When an + amount of time is given, only the sum of standard time and this + amount matters. + + FORMAT The format for time zone abbreviations. The pair of characters + %s shows where to put the time zone abbreviation's variable + part, which is taken from the LETTER/S field of the + corresponding rule; any timestamps that precede the earliest + rule use the LETTER/S of the earliest standard-time rule (which + in this case must exist). Alternatively, a format can use the + pair of characters %z to stand for the UT offset in the form + +-hh, +-hhmm, or +-hhmmss, using the shortest form that does not + lose information, where hh, mm, and ss are the hours, minutes, + and seconds east (+) or west (-) of UT. Alternatively, a slash + (/) separates standard and daylight abbreviations. To conform + to POSIX, a time zone abbreviation should contain only + alphanumeric ASCII characters, "+" and "-". By convention, the + time zone abbreviation "-00" is a placeholder that means local + time is unspecified. UNTIL The time at which the UT offset or the rule(s) change for a location. It takes the form of one to four fields YEAR [MONTH @@ -369,7 +372,7 @@ FILES Rule US 1967 1973 - Apr lastSun 2:00 1:00 D # Zone NAME STDOFF RULES FORMAT [UNTIL] Zone America/Menominee -5:00 - EST 1973 Apr 29 2:00 - -6:00 US C%sT + -6:00 US C%sT Here, an incorrect reading would be there were two clock changes on 1973-04-29, the first from 02:00 EST (-05) to 01:00 CST (-06), and the @@ -421,14 +424,14 @@ FILES second time given by the other fields should be interpreted as local (wall clock) time. - Rolling leap seconds were implemented back when it was not clear - whether common practice was rolling or stationary, with concerns that - one would see Times Square ball drops where there'd be a "3... 2... - 1... leap... Happy New Year" countdown, placing the leap second at - midnight New York time rather than midnight UTC. However, this - countdown style does not seem to have caught on, which means rolling - leap seconds are not used in practice; also, they are not supported if - the -r option is used. + Rolling leap seconds would let one see Times Square ball drops where + there'd be a "3... 2... 1... leap... Happy New Year" countdown, placing + the leap second at midnight New York time rather than midnight UTC. + Although stationary leap seconds are the common practice, rolling leap + seconds can be useful in specialized applications like SMPTE timecodes + that may prefer to put leap second discontinuities at the end of a + local broadcast day. However, rolling leap seconds are not supported + if the -r option is used. The expiration line, if present, has the form: @@ -442,7 +445,7 @@ FILES in UTC for the leap second table. EXTENDED EXAMPLE - Here is an extended example of zic input, intended to illustrate many + Here is an extended example of zic input, intended to illustrate many of its features. # Rule NAME FROM TO - IN ON AT SAVE LETTER/S @@ -463,29 +466,29 @@ EXTENDED EXAMPLE Link Europe/Zurich Europe/Vaduz - In this example, the EU rules are for the European Union and for its - predecessor organization, the European Communities. The timezone is - named Europe/Zurich and it has the alias Europe/Vaduz. This example - says that Zurich was 34 minutes and 8 seconds east of UT until - 1853-07-16 at 00:00, when the legal offset was changed to 7 degrees 26 - minutes 22.50 seconds, which works out to 0:29:45.50; zic treats this - by rounding it to 0:29:46. After 1894-06-01 at 00:00 the UT offset - became one hour and Swiss daylight saving rules (defined with lines - beginning with "Rule Swiss") apply. From 1981 to the present, EU - daylight saving rules have applied, and the UTC offset has remained at + In this example, the EU rules are for the European Union and for its + predecessor organization, the European Communities. The timezone is + named Europe/Zurich and it has the alias Europe/Vaduz. This example + says that Zurich was 34 minutes and 8 seconds east of UT until + 1853-07-16 at 00:00, when the legal offset was changed to 7 degrees 26 + minutes 22.50 seconds, which works out to 0:29:45.50; zic treats this + by rounding it to 0:29:46. After 1894-06-01 at 00:00 the UT offset + became one hour and Swiss daylight saving rules (defined with lines + beginning with "Rule Swiss") apply. From 1981 to the present, EU + daylight saving rules have applied, and the UTC offset has remained at one hour. In 1941 and 1942, daylight saving time applied from the first Monday in - May at 01:00 to the first Monday in October at 02:00. The pre-1981 EU - daylight-saving rules have no effect here, but are included for + May at 01:00 to the first Monday in October at 02:00. The pre-1981 EU + daylight-saving rules have no effect here, but are included for completeness. Since 1981, daylight saving has begun on the last Sunday - in March at 01:00 UTC. Until 1995 it ended the last Sunday in - September at 01:00 UTC, but this changed to the last Sunday in October + in March at 01:00 UTC. Until 1995 it ended the last Sunday in + September at 01:00 UTC, but this changed to the last Sunday in October starting in 1996. - For purposes of display, "LMT" and "BMT" were initially used, - respectively. Since Swiss rules and later EU rules were applied, the - time zone abbreviation has been CET for standard time and CEST for + For purposes of display, "LMT" and "BMT" were initially used, + respectively. Since Swiss rules and later EU rules were applied, the + time zone abbreviation has been CET for standard time and CEST for daylight saving time. FILES @@ -496,15 +499,15 @@ FILES Default timezone information directory. NOTES - For areas with more than two types of local time, you may need to use - local standard time in the AT field of the earliest transition time's - rule to ensure that the earliest transition time recorded in the + For areas with more than two types of local time, you may need to use + local standard time in the AT field of the earliest transition time's + rule to ensure that the earliest transition time recorded in the compiled file is correct. - If, for a particular timezone, a clock advance caused by the start of - daylight saving coincides with and is equal to a clock retreat caused - by a change in UT offset, zic produces a single transition to daylight - saving at the new UT offset without any change in local (wall clock) + If, for a particular timezone, a clock advance caused by the start of + daylight saving coincides with and is equal to a clock retreat caused + by a change in UT offset, zic produces a single transition to daylight + saving at the new UT offset without any change in local (wall clock) time. To get separate transitions use multiple zone continuation lines specifying transition instants using universal time. |