Tribblix: manual page: time.1

TIME(1) User Commands TIME(1)

NAME

time - time a simple command

SYNOPSIS

time [-p] utility [argument]...

DESCRIPTION

The time utility invokes utility operand with argument, and writes a
message to standard error that lists timing statistics for utility.
The message includes the following information:

o The elapsed (real) time between invocation of utility and
its termination.

o The User CPU time, equivalent to the sum of the tms_utime
and tms_cutime fields returned by the times(2) function
for the process in which utility is executed.

o The System CPU time, equivalent to the sum of the
tms_stime and tms_cstime fields returned by the times()
function for the process in which utility is executed.

When time is used as part of a pipeline, the times reported are
unspecified, except when it is the sole command within a grouping
command in that pipeline. For example, the commands on the left are
unspecified; those on the right report on utilities a and c,
respectively:

time a | b | c { time a } | b | c
a | b | time c a | b | (time c)

OPTIONS

The following option is supported:

-p
Writes the timing output to standard error in the following
format:

real %f\nuser %f\nsys %f\n < real seconds>, <user seconds>,
<system seconds>

OPERANDS

The following operands are supported:

utility
The name of the utility that is to be invoked.

argument
Any string to be supplied as an argument when invoking
utility.

USAGE

The time utility returns exit status 127 if an error occurs so that
applications can distinguish "failure to find a utility" from
"invoked utility exited with an error indication." The value 127 was
chosen because it is not commonly used for other meanings. Most
utilities use small values for "normal error conditions" and the
values above 128 can be confused with termination due to receipt of a
signal. The value 126 was chosen in a similar manner to indicate that
the utility could be found, but not invoked.

EXAMPLES

Example 1: Using the time command

It is frequently desirable to apply time to pipelines or lists of
commands. This can be done by placing pipelines and command lists in
a single file. This single file can then be invoked as a utility, and
the time applies to everything in the file.

Alternatively, the following command can be used to apply time to a
complex command:

example% time sh -c 'complex-command-line'

Example 2: Using time in the csh shell

The following two examples show the differences between the csh
version of time and the version in /usr/bin/time. These examples
assume that csh is the shell in use.

example% time find / -name csh.1 -print
/usr/share/man/man1/csh.1
95.0u 692.0s 1:17:52 16% 0+0k 0+0io 0pf+0w

See csh(1) for an explanation of the format of time output.

example% /usr/bin/time find / -name csh.1 -print
/usr/share/man/man1/csh.1
real 1:23:31.5
user 1:33.2
sys 11:28.2

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment
variables that affect the execution of time: LANG, LC_ALL, LC_CTYPE,
LC_MESSAGES, LC_NUMERIC, NLSPATH, and PATH.

EXIT STATUS

If utility is invoked, the exit status of time will be the exit
status of utility. Otherwise, the time utility will exit with one of
the following values:

1-125
An error occurred in the time utility.

126
utility was found but could not be invoked.

127
utility could not be found.

ATTRIBUTES

NOTES

When the time command is run on a multiprocessor machine, the total
of the values printed for user and sys can exceed real. This is
because on a multiprocessor machine it is possible to divide the task
between the various processors.

When the command being timed is interrupted, the timing values
displayed may not always be accurate.

BUGS

Elapsed time is accurate to the second, while the CPU times are
measured to the 100th second. Thus the sum of the CPU times can be up
to a second larger than the elapsed time.

February 1, 1995 TIME(1)