because formatting times should be easy, like ruby's strftime

strftime:f(now(), "Printed on %m/%d/%Y").    %=> "Printed on 11/19/2007"
strftime:f(now(), "at %I:%M%p").             %=> "at 08:37AM"
strftime:f(now(), "at %I:%M%p", universal).  %=> "at 02:37PM"
strftime:f(now(), "%D-%T.%N").               %=> "11/19/2007-08:38:02.445443"

strftime:f({epoch, os:system_time(1)},"%a, %d-%b-%Y %H:%M:%S GMT", universal).

strftime:f/2 uses system local time

strftime:f/3 allows you to specify 'local' or 'universal' as third argument.

strftime:f(now(), FormatString)

• %a - The abbreviated weekday name ('Sun')
• %A - The full weekday name ('Sunday')
• %b - The abbreviated month name ('Jan')
• %B - The full month name ('January')
• %C - Century (20 in 2009)
• %d - Day of the month (01..31)
• %D - Date (%m/%d/%y)
• %e - Day of the month, blank-padded ( 1..31)
• %F - Equivalent to %Y-%m-%d (the ISO 8601 date format)
• %h - Equivalent to %b
• %H - Hour of the day, 24-hour clock (00..23)
• %I - Hour of the day, 12-hour clock (01..12)
• %k - hour, 24-hour clock, blank-padded ( 0..23)
• %l - hour, 12-hour clock, blank-padded ( 0..12)
• %L - Millisecond of the second (000..999)
• %m - Month of the year (01..12)
• %M - Minute of the hour (00..59)
• %N - Fractional seconds digits
• %p - Meridian indicator ('AM' or 'PM')
• %P - Meridian indicator ('am' or 'pm')
• %r - time, 12-hour (same as %I:%M:%S %p)
• %R - time, 24-hour (%H:%M)
• %s - Number of seconds since 1970-01-01 00:00:00 UTC.
• %S - Second of the minute (00..60)
• %T - time, 24-hour (%H:%M:%S)
• %u - Day of the week as a decimal, Monday being 1. (1..7)
• %v - VMS date (%e-%b-%Y)
• %w - Day of the week (Sunday is 0, 0..6)
• %y - Year without a century (00..99)
• %Y - Year with century
• %% - Literal '%' character