-u/--utc selects UTC. Otherwise TZ selects a named TZif zone, anabsolute TZif path, or a POSIX timezone with explicit DST rules. Withno TZ, /etc/localtime is used. TZDIR changes the named-zone directory.Missing/invalid timezone data fails explicitly; on Windows use -u, aPOSIX TZ value or a TZif file when no timezone database is installed.
-d/--date accepts YYYY-MM-DD (local midnight), localYYYY-MM-DDTHH:MM:SS[.fraction] (a space may replace T), or @SECONDS,including signed fractions of up to nine digits. Input timezone suffixesare not supported; select the zone with TZ or -u.DST gaps and ambiguous local times arerejected; use an epoch timestamp to choose an exact instant.-I/--iso-8601 accepts date, hours, minutes, seconds or ns.-R/--rfc-email emits an RFC email timestamp. These output selectorscannot be combined with each other or a +FORMAT operand.
Supported format fields are %Y %y %m %d %e %H %M %S %j %a %A %b %h %B%F %T %R %s %N %z %Z %%. Names use the C locale. Other known GNU fieldsand format modifiers are rejected. The current clock has millisecondprecision; supplied fractional epochs retain nanoseconds. Relative-dateparsing, leap-second TZif files and setting the system clock are notimplemented. The released date/time API accepts offsets within ±18 hours;larger offsets fail explicitly. --help and --version are available.
Standalone --version prints exactly date 0.1.2 followed by onenewline. Standalone --help starts with Usage: date, lists bothmetadata options, and ends with a newline. Both write to stdout, leave stdinunread, and exit with status 0. Exact-version publication and verificationremain recorded separately in the support record.