posix man page for time

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 correspond-
       ing 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 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.1-2008 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)

OPTIONS
       The time utility shall conform to the Base Definitions volume of POSIX.1-2008, 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 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.

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
		 POSIX.1-2008,	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.1-2008, 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
user %f
sys %f
", <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.

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 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.

EXAMPLES
       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'

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 POSIX.1-2008 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.1-2008.

       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.1-2008.

       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 pipe-
       line timing (because the constituent processes are not all owned by the same parent process, as allowed by POSIX), it did not  seem  worth-
       while 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
       Chapter 2, Shell Command Language, sh

       The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1-2008, times()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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						       2013								  TIME(1P)