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Unix time [a] is a date and time representation widely used in computing. It measures time by the number of non-leap seconds that have elapsed since 00:00:00 UTC on 1 January 1970, the Unix epoch. For example, at midnight on 1 January 2010, Unix time was 1262304000. Unix time originated as the system time of Unix operating systems.
Software timekeeping systems vary widely in the resolution of time measurement; some systems may use time units as large as a day, while others may use nanoseconds.For example, for an epoch date of midnight UTC (00:00) on 1 January 1900, and a time unit of a second, the time of the midnight (24:00) between 1 January 1900 and 2 January 1900 is represented by the number 86400, the number of ...
Many computer systems measure time and date using Unix time, an international standard for digital timekeeping. Unix time is defined as the number of seconds elapsed since 00:00:00 UTC on 1 January 1970 (an arbitrarily chosen time based on the creation of the first Unix system), which has been dubbed the Unix epoch. [6]
System time can be converted into calendar time, which is a form more suitable for human comprehension. For example, the Unix system time 1 000 000 000 seconds since the beginning of the epoch translates into the calendar time 9 September 2001 01:46:40 UT.
The Unix command time prints CPU time and elapsed real time for the execution of a Unix command (or pipeline). Note that many command-line shells have their own implementation of this command. To run the Unix program time , we provide its full path, /usr/bin/time :
Identifier Description Time manipulation difftime: computes the difference in seconds between two time_t values : time: returns the current time of the system as a time_t value, number of seconds, (which is usually time since an epoch, typically the Unix epoch).
The reported time is a time used by both seq and wc -l added up. Format of the output can be adjusted using TIMEFORMAT variable. The time is not a builtin, but a special keyword, and can't be treated as a function or command. It also ignores pipeline redirections (even when executed as time -p, unless entire Bash is run in "POSIX mode").
For example, Unix time is represented as the number of seconds since 00:00:00 UTC on 1 January 1970, not counting leap seconds. An epoch in astronomy is a reference time used for consistency in calculation of positions and orbits. A common astronomical epoch is J2000, which is noon on January 1, 2000, Terrestrial Time.