man-page time

   Controls automatic timing of commands, and the line displayed by a 
   built-in time command. The value can consist of zero, one, or two 
   The first word is the threshhold for automatic timing, measured in CPU
   seconds; for any command that takes at least that many CPU seconds, the 
   shell displays a line showing the timing information when that command 
   The second word is a string, enclosed in ' ' (single quotes) or " " 
   (double quotes), specifying the timing line to be displayed; it con- 
   trols both the automatic display and the output of the time command. 
   The string can contain any combination of text as well as the following 
   specifiers, which must be uppercase characters and preceded by a % 
   (percent sign) as shown. Sequences such as \n are not treated as spe- 
   cial characters in the string. 
   %D Kilobytes of data space. 
   %E Elapsed time, measured in seconds. 
   %F Number of page faults. 
   %I Number of blocks read during I/O operations. 
   %K Kilobytes of stack space. %M Total kilobytes of memory. 
   %O Number of blocks written during I/O operations. 
   %P CPU time (both system and user) as a percentage of elapsed time. 
   %S System time: CPU seconds used by system calls. 
   %U User time: CPU seconds used by the process outside of system calls. 
   %W Number of times the process was swapped. 
   %X Kilobytes of text space. 
   If the first word is zero or if the time variable is set with no value, 
   every command is timed. The default string displayed, when the second 
   word is not supplied, is as follows: 
       %Uu %Ss %E %P% %X+%Dk %I+%Oio %Fpf+%Ww