время простая команда (time a simple command)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
time — time a simple command
Синопсис (Synopsis)
time [-p] utility [argument...]
Описание (Description)
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 POSIX.1‐2017 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 Section 2.9.4.1, 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)
Параметры (Options)
The time utility shall conform to the Base Definitions volume of
POSIX.1‐2017, 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.
Операнды (Operands)
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 Section 2.14, 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.
Стандартный ввод (Stdin)
Not used.
Входные файлы (Input files)
None.
Переменные окружения (Environment variables)
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 POSIX.1‐2017, 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 POSIX.1‐2017, Chapter 8, Environment
Variables.
Асинхронные события (Asynchronous events)
Default.
Стандартный вывод (Stdout)
Not used.
Стандартный вывод сообщений (Stderr)
If the utility utility is invoked, the standard error shall be
used to write the timing statistics and may be used to write a
diagnostic message if the utility terminates abnormally;
otherwise, the standard error shall be used to write diagnostic
messages and may also be used to write the timing statistics.
If -p is specified, the following format shall be used for the
timing statistics 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. The
implementation may also prepend a single empty line before the
format shown here.
Выходные файлы (Output files)
None.
Расширенное описание (Extended description)
None.
Статус выхода (Exit)
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.
Последствия ошибок (Consequences of errors)
Default.
The following sections are informative.
Использование в приложениях (Application usage)
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.
Примеры (Examples)
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'
Обоснование (Rationale)
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 POSIX.1‐2017 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 POSIX.1‐2017.
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 POSIX.1‐2017.
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.
Будущие направления (Future directions)
None.
Смотри также (See also)
Chapter 2, Shell Command Language, sh(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, times(3p)
