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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 dif-
       fer (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 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 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 unspecified, 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 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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the prece-
              dence 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 exam-
              ple, 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 Defini-
              tions 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 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.

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 dis-
       tinction  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 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 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 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 timing (because  the  con-
       stituent  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
       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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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(1P)