Returns a character string of the current system date and time.
The string has the form "Fri Aug 20 11:11:00 1999", i.e.,
length 24, since it relies on POSIX's ctime ensuring the above
fixed format. Timezone and Daylight Saving Time are taken account of,
but not indicated in the result.
The day and month abbreviations are always in English, irrespective
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
The New S Language.
Wadsworth & Brooks/Cole.