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+'\" 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
+man page format. To report such errors, see
+https://www.kernel.org/doc/man-pages/reporting_bugs.html .