# time

## 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.
    


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