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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
       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.1‐2017 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.1‐2017,  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.1‐2017, 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.1‐2017, Chapter 8, Environment Variables.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       If the utility utility is invoked, the standard error shall be used to write the  timing  statistics  and
       may  be  used to write a diagnostic message if the utility terminates abnormally; otherwise, the standard
       error shall be used to write diagnostic messages and may also be used to write the timing statistics.

       If -p is specified, the following format shall be used for the timing statistics 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. 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.1‐2017 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.1‐2017.

       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.1‐2017.

       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.

SEE ALSO

       Chapter 2, Shell Command Language, sh

       The  Base  Definitions  volume  of  POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility
       Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2017, times()

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

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