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TIME(P)			   POSIX Programmer's Manual		       TIME(P)

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(P)
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