|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
TIME(1P) POSIX Programmer's Manual TIME(1P)
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.
time — time a simple command
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 POSIX.1‐2008 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)
The time utility shall conform to the Base Definitions volume of
POSIX.1‐2008, 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
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.
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 POSIX.1‐2008, 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.1‐2008, 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. The implementation may also prepend
a single empty line before 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 POSIX.1‐2008 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.1‐2008.
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.1‐2008.
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.
Chapter 2, Shell Command Language, sh(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2008, times(3p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TIME(1P)
|
HTML rendering created 2018-02-02 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH.
|
|