Originální popis anglicky:
time - time a simple command
Návod, kniha: POSIX Programmer's Manual
time [-p] utility
[argument... ]
The
time utility shall invoke the utility named by the
utility
operand with arguments supplied as the
argument operands and write a
message to standard error that lists timing statistics for the utility. The
message shall include the following information:
- *
- The elapsed (real) time between invocation of
utility and its termination.
- *
- The User CPU time, equivalent to the sum of the
tms_utime and tms_cutime fields returned by the
times() function defined in the System Interfaces volume of
IEEE Std 1003.1-2001 for the process in which utility
is executed.
- *
- 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.
The precision of the timing shall be no less than the granularity defined for
the size of the clock tick unit on the system, but the results shall be
reported in terms of standard time units (for example, 0.02 seconds,
00:00:00.02, 1m33.75s, 365.21 seconds), not numbers of clock ticks.
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 (see
Grouping Commands ) 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)
The
time utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
- -p
- Write the timing output to standard error in the format
shown in the STDERR section.
The following operands shall be supported:
- utility
- The name of a utility that is to be invoked. If the
utility operand names any of the special built-in utilities in
Special Built-In Utilities , the results are undefined.
- argument
- Any string to be supplied as an argument when invoking the
utility named by the utility operand.
Not used.
None.
The following environment variables shall affect the execution of
time:
- LANG
- Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
- LC_ALL
- If set to a non-empty string value, override the values of
all the other internationalization variables.
- LC_CTYPE
- Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
- LC_MESSAGES
- Determine the locale that should be used to affect the
format and contents of diagnostic and informative messages written to
standard error.
- LC_NUMERIC
-
Determine the locale for numeric formatting.
- NLSPATH
- Determine the location of message catalogs for the
processing of LC_MESSAGES .
- PATH
- Determine the search path that shall be used to locate the
utility to be invoked; see the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
Default.
Not used.
The standard error shall be used to write the timing statistics. If
-p is
specified, the following format shall be used in the POSIX locale:
"real %f\nuser %f\nsys %f\n", <real seconds>, <user seconds>,
<system seconds>
where each floating-point number shall be expressed in seconds. The precision
used may be less than the default six digits of
%f , but shall be
sufficiently precise to accommodate the size of the clock tick on the system
(for example, if there were 60 clock ticks per second, at least two digits
shall follow the radix character). The number of digits following the radix
character shall be no less than one, even if this always results in a trailing
zero. The implementation may append white space and additional information
following the format shown here.
None.
None.
If the
utility utility is invoked, the exit status of
time shall
be the exit status of
utility; otherwise, the
time utility shall
exit with one of the following values:
- 1-125
- An error occurred in the time utility.
- 126
- The utility specified by utility was found but could
not be invoked.
- 127
- The utility specified by utility could not be found.
Default.
The following sections are informative.
The
command,
env,
nice,
nohup,
time, and
xargs utilities have been specified to use exit code 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. Some scripts
produce meaningful error messages differentiating the 126 and 127 cases. The
distinction between exit codes 126 and 127 is based on KornShell practice that
uses 127 when all attempts to
exec the utility fail with [ENOENT], and
uses 126 when any attempt to
exec the utility fails for any other
reason.
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 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:
time sh -c 'complex-command-line'
When the
time utility was originally proposed to be included in the
ISO POSIX-2:1993 standard, questions were raised about its suitability
for inclusion on the grounds that it was not useful for conforming
applications, specifically:
- *
- The underlying CPU definitions from the System Interfaces
volume of IEEE Std 1003.1-2001 are vague, so the numeric
output could not be compared accurately between systems or even between
invocations.
- *
- The creation of portable benchmark programs was outside the
scope this volume of IEEE Std 1003.1-2001.
However,
time does fit in the scope of user portability. Human judgement
can be applied to the analysis of the output, and it could be very useful in
hands-on debugging of applications or in providing subjective measures of
system performance. Hence it has been included in this volume of
IEEE Std 1003.1-2001.
The default output format has been left unspecified because historical
implementations differ greatly in their style of depicting this numeric
output. The
-p option was invented to provide scripts with a common
means of obtaining this information.
In the KornShell,
time is a shell reserved word that can be used to time
an entire pipeline, rather than just a simple command. The POSIX definition
has been worded to allow this implementation. Consideration was given to
invalidating this approach because of the historical model from the C shell
and System V shell. However, since the System V
time utility
historically has not produced accurate results in pipeline timing (because the
constituent processes are not all owned by the same parent process, as allowed
by POSIX), it did not seem worthwhile to break historical KornShell usage.
The term
utility is used, rather than
command, to highlight the
fact that shell compound commands, pipelines, special built-ins, and so on,
cannot be used directly. However,
utility includes user application
programs and shell scripts, not just the standard utilities.
None.
Shell Command Language ,
sh , the System Interfaces volume of
IEEE Std 1003.1-2001,
times()
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html
.
