Returns the number of seconds since January 1st, 1970, Midnight, in Greenwich (GMT). Also known as "Unix time", "timestamp" or "epoch".

Example:

 clock seconds

on Dec 10 2004, 11:44:22, returns

 1102686262

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See also: [clock]

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[LV] Is the epoch the same on all platforms and operating systems?

[MSW] Due to the source, at least under unix and windows the epoch is 1970-01-01 @ midnight. Under mac the epoch starts (due to the comments)  Midnight Jan 1, 1904. mac/tclMacTime.c adds another tcl_mac_epoch_offset which is initialized by _mac_msl_epoch_offset_ if defined (and 0 otherwise), which I assume brings the Mac epoch in sync with the unix epoch. (I don't have a Mac handy to test...)

[Lars H]: It's better to say 00:00 than midnight, since each day also has a midnight at 24:00. But there is also another ambiguity, with respect to the time zone. When I do [[clock format 0]] I get Thu Jan 01 01:00:00 CET 1970, which seems to indicate that the epoch is from 1970-01-01 T 00:00 Z (i.e., it's the UTC/GMT midnight). Is this true on all platforms which use the 1970 epoch?

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[FPX] Anybody knows the difference between Unix and Macintosh epoch? I was stumbling about this recently, requiring a platform-independent "seconds since epoch" value. Seems like the best we can do is

  set sse [clock seconds]
  if {[string equal $::tcl_platform(platform) "macintosh"]} {
    incr sse <seconds between 1904 1970>
  }

Is the constant simply (negative) 2082844800, i.e., 60*60*24*(365*66+17), 66 years with 17 leap years, or do we also have to factor in some number of leap seconds?

[Lars H]: [Alpha] does the following [http://cvs.sourceforge.net/viewcvs.py/alphatcl/Tcl/SystemCode/CorePackages/ISOTime.tcl?view=log]:
  # Convert seconds from 'epoch' to the unix epoch (used by 'clock').
  proc ISOTime::fromEpoch {epoch when} {
    global ISOTime::systemEpoch
    
    if {$epoch == ""} {
      set epoch [set ISOTime::systemEpoch]
    }
    
    if {$epoch == "unix"} {
      return $when
    } elseif {$epoch == "mac"} {
      set when [expr $when + [clock scan "1904-01-01Z00:00:00"]]
      return [expr $when - [ISOTime::ZoneOffset $when "unix"]]
    } else {
      error "ISOTime error: Unknown epoch \"$epoch\""
    }
  }
Anyway the problem of the mac epoch is 2004 getting rather academic.
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[RS]: Find out what your epoch is, without timezone offset, with
 clock format 0 -gmt 1
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[Category Date and Time]
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