time

TIME(1POSIX)               POSIX Programmer's Manual              TIME(1POSIX)



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.1‐2008 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.1‐2008, 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.1‐2008, 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.1‐2008, 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.
       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.1‐2008 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.1‐2008.

       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.1‐2008.

       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.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, times()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2013                         TIME(1POSIX)