'\" et
.TH TIME "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH 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.
.\"
.SH NAME
time
\(em time a simple command
.SH SYNOPSIS
.LP
.nf
time \fB[\fR-p\fB] \fIutility \fB[\fIargument\fR...\fB]\fR
.fi
.SH DESCRIPTION
The
.IR time
utility shall invoke the utility named by the
.IR utility
operand with arguments supplied as the
.IR argument
operands and write a message to standard error that lists timing
statistics for the utility. The message shall include the following
information:
.IP " *" 4
The elapsed (real) time between invocation of
.IR utility
and its termination.
.IP " *" 4
The User CPU time, equivalent to the sum of the
.IR tms_utime
and
.IR tms_cutime
fields returned by the
\fItimes\fR()
function defined in the System Interfaces volume of POSIX.1\(hy2017 for the process in which
.IR utility
is executed.
.IP " *" 4
The System CPU time, equivalent to the sum of the
.IR tms_stime
and
.IR tms_cstime
fields returned by the
\fItimes\fR()
function for the process in which
.IR utility
is executed.
.P
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.
.P
When
.IR 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
.IR "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
.BR a
and
.BR c ,
respectively:
.sp
.RS 4
.nf

time a | b | c    { time a; } | b | c
a | b | time c    a | b | (time c)
.fi
.P
.RE
.SH OPTIONS
The
.IR time
utility shall conform to the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.P
The following option shall be supported:
.IP "\fB\-p\fP" 10
Write the timing output to standard error in the format shown in the
STDERR section.
.SH OPERANDS
The following operands shall be supported:
.IP "\fIutility\fR" 10
The name of a utility that is to be invoked. If the
.IR utility
operand names any of the special built-in utilities in
.IR "Section 2.14" ", " "Special Built-In Utilities",
the results are undefined.
.IP "\fIargument\fR" 10
Any string to be supplied as an argument when invoking the utility
named by the
.IR utility
operand.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR time :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
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).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic and informative messages written to standard
error.
.IP "\fILC_NUMERIC\fP" 10
.br
Determine the locale for numeric formatting.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.IP "\fIPATH\fP" 10
Determine the search path that shall be used to locate the utility to
be invoked; see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables".
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
Not used.
.SH STDERR
If the
.IR 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.
.P
If
.BR \-p
is specified, the following format shall be used for the timing
statistics in the POSIX locale:
.sp
.RS 4
.nf

"real %f\enuser %f\ensys %f\en", <\fIreal seconds\fR>, <\fIuser seconds\fR>,
    <\fIsystem seconds\fR>
.fi
.P
.RE
.P
where each floating-point number shall be expressed in seconds. The
precision used may be less than the default six digits of
.BR %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.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
If the
.IR utility
utility is invoked, the exit status of
.IR time
shall be the exit status of
.IR utility ;
otherwise, the
.IR time
utility shall exit with one of the following values:
.IP "1\(hy125" 8
An error occurred in the
.IR time
utility.
.IP "\0\0126" 8
The utility specified by
.IR utility
was found but could not be invoked.
.IP "\0\0127" 8
The utility specified by
.IR utility
could not be found.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
The
.IR command ,
.IR env ,
.IR nice ,
.IR nohup ,
.IR time ,
and
.IR 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
.IR exec
the utility fail with
.BR [ENOENT] ,
and uses 126 when any attempt to
.IR exec
the utility fails for any other reason.
.SH EXAMPLES
It is frequently desirable to apply
.IR 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
.IR time
applies to everything in the file.
.P
Alternatively, the following command can be used to apply
.IR time
to a complex command:
.sp
.RS 4
.nf

time sh -c \(aq\fIcomplex-command-line\fP\(aq
.fi
.P
.RE
.SH RATIONALE
When the
.IR time
utility was originally proposed to be included in the ISO\ POSIX\(hy2:\|1993 standard,
questions were raised about its suitability for inclusion on
the grounds that it was not useful for conforming applications,
specifically:
.IP " *" 4
The underlying CPU definitions from the System Interfaces volume of POSIX.1\(hy2017 are
vague, so the numeric output could not be compared accurately between
systems or even between invocations.
.IP " *" 4
The creation of portable benchmark programs was outside the scope this volume of POSIX.1\(hy2017.
.P
However,
.IR 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\(hy2017.
.P
The default output format has been left unspecified because historical
implementations differ greatly in their style of depicting this numeric
output. The
.BR \-p
option was invented to provide scripts with a common means of obtaining
this information.
.P
In the KornShell,
.IR 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
.IR 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.
.P
The term
.IR utility
is used, rather than
.IR command ,
to highlight the fact that shell compound commands, pipelines, special
built-ins, and so on, cannot be used directly.
However,
.IR utility
includes user application programs and shell scripts, not just the
standard utilities.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "Chapter 2" ", " "Shell Command Language",
.IR "\fIsh\fR\^"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables",
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fItimes\fR\^(\|)"
.\"
.SH COPYRIGHT
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 .
.PP
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
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .