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

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
              operand  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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