time(1p) — Linux manual page


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

        *  The elapsed (real) time between invocation of utility and its

        *  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, 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.1‐2017, 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         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



       The following environment variables shall affect the execution of

       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).

                 Determine the locale that should be used to affect the
                 format and contents of diagnostic and informative
                 messages written to standard error.

                 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



STDOUT         top

       Not used.

STDERR         top

       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         top




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.



       The following sections are informative.


       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

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.1‐2017 are vague, so the numeric output could
           not be compared accurately between systems or even between

        *  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

       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.



SEE ALSO         top

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

       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(3p)

COPYRIGHT         top

       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 .

       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               2017                          TIME(1P)