Check the default output format of
# time real 0m0.000s user 0m0.000s sys 0m0.000s
You can use
-p option to output in
# time -p real 0.00 user 0.00 sys 0.00
bash source code, we know the the definitions of these two formats:
#define POSIX_TIMEFORMAT "real %2R\nuser %2U\nsys %2S" #define BASH_TIMEFORMAT "\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS"
To decipher the meanings of them, we need to refer bash manual:
The value of this parameter is used as a format string specifying how the timing information for pipelines prefixed with the time reserved word should be displayed. The ‘%’ character introduces an escape sequence that is expanded to a time value or other information. The escape sequences and their meanings are as follows; the braces denote optional portions.
A literal ‘%’.
The elapsed time in seconds.
The number of CPU seconds spent in user mode.
The number of CPU seconds spent in system mode.
The CPU percentage, computed as (%U + %S) / %R.
The optional p is a digit specifying the precision, the number of fractional digits after a decimal point. A value of 0 causes no decimal point or fraction to be output. At most three places after the decimal point may be specified; values of p greater than 3 are changed to 3. If p is not specified, the value 3 is used.
The optional l specifies a longer format, including minutes, of the form MMmSS.FFs. The value of p determines whether or not the fraction is included.
POSIX_TIMEFORMAT as an example:
%2R denotes using second as time unit, and the precision is two digits after a decimal point;
%2S are similar.
Now you can comprehend the output of
time, correct? Try using
BASH_TIMEFORMAT as a practice.