os/strftime

    cfunction
    src/core/os.c on line 1929, column 1

    (os/strftime fmt &opt time local)

    Format the given time as a string, or the current time if `time` is 
    not given. The time is formatted according to the same rules as the 
    ISO C89 function strftime(). The time is formatted in UTC unless 
    `local` is truthy, in which case the date is formatted for the 
    local timezone. You can set local timezone by setting TZ 
    environment variable. See tzset(<time.h>) or _tzset(<time.h>) for 
    further details.