man-pages/man1p/time.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "TIME" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" time 
.SH NAME
time \- time a simple command
.SH SYNOPSIS
.LP
\fBtime\fP \fB[\fP\fB-p\fP\fB]\fP \fIutility\fP
\fB[\fP\fIargument\fP\fB...\fP\fB]\fP\fB\fP
.SH DESCRIPTION
.LP
The \fItime\fP utility shall invoke the utility named by the \fIutility\fP
operand with arguments supplied as the
\fIargument\fP operands and write a message to standard error that
lists timing statistics for the utility. The message shall
include the following information:
.IP " *" 3
The elapsed (real) time between invocation of \fIutility\fP and its
termination.
.LP
.IP " *" 3
The User CPU time, equivalent to the sum of the \fItms_utime\fP and
\fItms_cutime\fP fields returned by the \fItimes\fP() function defined
in the System Interfaces volume of IEEE\ Std\ 1003.1-2001 for
the process in which \fIutility\fP is executed.
.LP
.IP " *" 3
The System CPU time, equivalent to the sum of the \fItms_stime\fP
and \fItms_cstime\fP fields returned by the \fItimes\fP() function
for the process in which \fIutility\fP is executed.
.LP
.LP
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.
.LP
When \fItime\fP is used as part of a pipeline, the times reported
are unspecified, except when it is the sole command within a
grouping command (see \fIGrouping Commands\fP ) in that pipeline.
For example, the
commands on the left are unspecified; those on the right report on
utilities \fBa\fP and \fBc\fP, respectively:
.sp
.RS
.nf

\fBtime a | b | c    { time a } | b | c
a | b | time c    a | b | (time c)
\fP
.fi
.RE
.SH OPTIONS
.LP
The \fItime\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option shall be supported:
.TP 7
\fB-p\fP
Write the timing output to standard error in the format shown in the
STDERR section.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIutility\fP
The name of a utility that is to be invoked. If the \fIutility\fP
operand names any of the special built-in utilities in \fISpecial
Built-In Utilities\fP , the results are undefined.
.TP 7
\fIargument\fP
Any string to be supplied as an argument when invoking the utility
named by the \fIutility\fP operand.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fItime\fP:
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic and informative messages written to
standard error.
.TP 7
\fILC_NUMERIC\fP
.sp
Determine the locale for numeric formatting.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPATH\fP
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.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used to write the timing statistics. If
\fB-p\fP is specified, the following format shall be used
in the POSIX locale:
.sp
.RS
.nf

\fB"real %f\\nuser %f\\nsys %f\\n", <\fP\fIreal seconds\fP\fB>, <\fP\fIuser seconds\fP\fB>,
    <\fP\fIsystem seconds\fP\fB>
\fP
.fi
.RE
.LP
where each floating-point number shall be expressed in seconds. The
precision used may be less than the default six digits of
\fB%f\fP , 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.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
If the \fIutility\fP utility is invoked, the exit status of \fItime\fP
shall be the exit status of \fIutility\fP; otherwise,
the \fItime\fP utility shall exit with one of the following values:
.TP 7
1-125
An error occurred in the \fItime\fP utility.
.TP 7
\ \ 126
The utility specified by \fIutility\fP was found but could not be
invoked.
.TP 7
\ \ 127
The utility specified by \fIutility\fP could not be found.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fIcommand\fP, \fIenv\fP, \fInice\fP, \fInohup\fP, \fItime\fP,
and \fIxargs\fP 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
\fIexec\fP the utility fail with [ENOENT], and uses 126 when any attempt
to \fIexec\fP the utility fails for any other
reason.
.SH EXAMPLES
.LP
It is frequently desirable to apply \fItime\fP 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 \fItime\fP applies to everything in the
file.
.LP
Alternatively, the following command can be used to apply \fItime\fP
to a complex command:
.sp
.RS
.nf

\fBtime sh -c '\fP\fIcomplex-command-line\fP\fB'
\fP
.fi
.RE
.SH RATIONALE
.LP
When the \fItime\fP 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:
.IP " *" 3
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.
.LP
.IP " *" 3
The creation of portable benchmark programs was outside the scope
this volume of IEEE\ Std\ 1003.1-2001.
.LP
.LP
However, \fItime\fP 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.
.LP
The default output format has been left unspecified because historical
implementations differ greatly in their style of
depicting this numeric output. The \fB-p\fP option was invented to
provide scripts with a common means of obtaining this
information.
.LP
In the KornShell, \fItime\fP 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 \fItime\fP 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.
.LP
The term \fIutility\fP is used, rather than \fIcommand\fP, to highlight
the fact that shell compound commands, pipelines,
special built-ins, and so on, cannot be used directly. However, \fIutility\fP
includes user application programs and shell
scripts, not just the standard utilities.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIShell Command Language\fP , \fIsh\fP , the System Interfaces
volume of IEEE\ Std\ 1003.1-2001, \fItimes\fP()
.SH 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 .