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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 |
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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.1‐2017 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)
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.
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.1‐2017, 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.
Default.
Not used.
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.
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.1‐2017 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.
None.
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)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 TIME(1P)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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