coreutils: Seconds since the Epoch
29.9 Seconds since the Epoch
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If you precede a number with ‘@’, it represents an internal timestamp as
a count of seconds. The number can contain an internal decimal point
(either ‘.’ or ‘,’); any excess precision not supported by the internal
representation is truncated toward minus infinity. Such a number cannot
be combined with any other date item, as it specifies a complete
timestamp.
Internally, computer times are represented as a count of seconds
since an epoch—a well-defined point of time. On GNU and POSIX systems,
the epoch is 1970-01-01 00:00:00 UTC, so ‘@0’ represents this time, ‘@1’
represents 1970-01-01 00:00:01 UTC, and so forth. GNU and most other
POSIX-compliant systems support such times as an extension to POSIX,
using negative counts, so that ‘@-1’ represents 1969-12-31 23:59:59 UTC.
Traditional Unix systems count seconds with 32-bit two’s-complement
integers and can represent times from 1901-12-13 20:45:52 through
2038-01-19 03:14:07 UTC. More modern systems use 64-bit counts of
seconds with nanosecond subcounts, and can represent all the times in
the known lifetime of the universe to a resolution of 1 nanosecond.
On most hosts, these counts ignore the presence of leap seconds. For
example, on most hosts ‘@915148799’ represents 1998-12-31 23:59:59 UTC,
‘@915148800’ represents 1999-01-01 00:00:00 UTC, and there is no way to
represent the intervening leap second 1998-12-31 23:59:60 UTC.
Info Catalog
coreutils: Pure numbers in date strings
coreutils: Date input formats
coreutils: Specifying time zone rules