TIME(1P) POSIX Programmer's Manual TIME(1P)
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.
NAME
time - time a simple command
SYNOPSIS
time [-p] utility [argument...]
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 mes-
sage shall include the following information:
* The elapsed (real) time between invocation of utility and its termi-
nation.
* 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 unspec-
ified, 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)
OPTIONS
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.
OPERANDS
The following operands shall be supported:
utility
The name of a utility that is to be invoked. If the utility op-
erand 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 util-
ity named by the utility operand.
STDIN
Not used.
INPUT FILES
None.
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
IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari-
ables 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 util-
ity to be invoked; see the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, Environment Variables.
ASYNCHRONOUS EVENTS
Default.
STDOUT
Not used.
STDERR
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 dig-
its 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.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
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.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
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 val-
ues for "normal error conditions" and the values above 128 can be con-
fused 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 differ-
entiating 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.
EXAMPLES
It is frequently desirable to apply time to pipelines or lists of com-
mands. 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'
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
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 judge-
ment 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 vol-
ume 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 tim-
ing (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.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language, sh, the System Interfaces volume of
IEEE Std 1003.1-2001, times()
COPYRIGHT
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 .
IEEE/The Open Group 2003 TIME(1P)
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