PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       time — time a simple command

SYNOPSIS         top

       time [−p] utility [argument...]

DESCRIPTION         top

       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         top

       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         top

       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         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       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         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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         top

       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         top

       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         top

       None.

SEE ALSO         top

       Chapter 2, Shell Command Language, sh(1p)

       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(3p)

COPYRIGHT         top

       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(1P)