Ubuntu Manpage: time - time a simple command

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 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 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 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
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
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.

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 .