#Bash 的 time 命令

TIME(1)                     General Commands Manual                    TIME(1)

NAME
       time - run programs and summarize system resource usage

SYNOPSIS
       time   [ -apqvV ] [ -f FORMAT ] [ -o FILE ]
              [ --append ] [ --verbose ] [ --quiet ] [ --portability ]
              [ --format=FORMAT ] [ --output=FILE ] [ --version ]
              [ --help ] COMMAND [ ARGS ]

DESCRIPTION
       time run the program COMMAND with any given arguments ARG....  When
       COMMAND finishes, time displays information about resources used by
       COMMAND (on the standard error output, by default).  If COMMAND exits
       with non-zero status, time displays a warning message and the exit
       status.

       time determines which information to display about the resources used
       by the COMMAND from the string FORMAT.  If no format is specified on
       the command line, but the TIME environment variable is set, its value
       is used as the format.  Otherwise, a default format built into time is
       used.

       Options to time must appear on the command line before COMMAND.
       Anything on the command line after COMMAND is passed as arguments to
       COMMAND.

OPTIONS
       -o FILE, --output=FILE
              Write  the  resource  use  statistics  to FILE instead of to the
              standard error stream.  By default, this  overwrites  the  file,
              destroying  the file's previous contents.  This option is useful
              for collecting information on interactive programs and  programs
              that produce output on the standard error stream.

       -a, --append
              Append  the  resource use information to the output file instead
              of overwriting it.  This option is only useful with the `-o'  or
              `--output' option.

       -f FORMAT, --format FORMAT
              Use  FORMAT  as  the  format  string that controls the output of
              time.  See the below more information.

       --help Print a summary of the command line options and exit.

       -p, --portability
              Use the following format  string,  for  conformance  with  POSIX
              standard 1003.2:
                        real %e
                        user %U
                        sys %S

       -v, --verbose
              Use  the  built-in verbose format, which displays each available
              piece of information on the program's resource use  on  its  own
              line, with an English description of its meaning.

       --quiet
              Do  not report the status of the program even if it is different
              from zero.

       -V, --version
              Print the version number of time and exit.

FORMATTING THE OUTPUT
       The format string FORMAT controls the contents of the time output.  The
       format string can  be  set  using  the  `-f'  or  `--format',  `-v'  or
       `--verbose',  or  `-p'  or  `--portability'  options.   If they are not
       given, but the TIME environment variable is set, its value is  used  as
       the  format string.  Otherwise, a built-in default format is used.  The
       default format is:
         %Uuser %Ssystem %Eelapsed %PCPU (%Xtext+%Ddata %Mmax)k
         %Iinputs+%Ooutputs (%Fmajor+%Rminor)pagefaults %Wswaps

       The  format  string   usually   consists   of   `resource   specifiers'
       interspersed  with  plain  text.   A  percent  sign (`%') in the format
       string causes the following character to be interpreted as  a  resource
       specifier,  which  is  similar  to  the  formatting  characters  in the
       printf(3) function.

       A backslash (`\') introduces a `backslash escape', which is  translated
       into  a  single  printing  character  upon  output.  `\t' outputs a tab
       character, `\n' outputs a newline, and `\\'  outputs  a  backslash.   A
       backslash followed by any other character outputs a question mark (`?')
       followed  by  a backslash, to indicate that an invalid backslash escape
       was given.

       Other text in the format string is copied verbatim to the output.  time
       always prints a newline after printing the resource use information, so
       normally format strings do not end with a newline character (or `\n').

       There are many resource specifications.  Not all resources are measured
       by all versions of Unix, so some of the values  might  be  reported  as
       zero.  Any character following a percent sign that is not listed in the
       table below causes a question mark (`?') to be output, followed by that
       character, to indicate that an invalid resource specifier was given.

       The  resource  specifiers,  which are a superset of those recognized by
       the tcsh(1) builtin `time' command, are:
              %      A literal `%'.
              C      Name and command line  arguments  of  the  command  being
                     timed.
              D      Average  size  of  the  process's  unshared data area, in
                     Kilobytes.
              E      Elapsed real (wall clock) time used by  the  process,  in
                     [hours:]minutes:seconds.
              F      Number  of  major,  or  I/O-requiring,  page  faults that
                     occurred while the process was running.  These are faults
                     where the page  has  actually  migrated  out  of  primary
                     memory.
              I      Number of file system inputs by the process.
              K      Average   total   (data+stack+text)  memory  use  of  the
                     process, in Kilobytes.
              M      Maximum resident set  size  of  the  process  during  its
                     lifetime, in Kilobytes.
              O      Number of file system outputs by the process.
              P      Percentage  of  the  CPU that this job got.  This is just
                     user + system times divided by the  total  running  time.
                     It also prints a percentage sign.
              R      Number  of minor, or recoverable, page faults.  These are
                     pages that are not valid (so they fault) but  which  have
                     not  yet  been  claimed by other virtual pages.  Thus the
                     data in the page is still valid  but  the  system  tables
                     must be updated.
              S      Total  number of CPU-seconds used by the system on behalf
                     of the process (in kernel mode), in seconds.
              U      Total  number  of  CPU-seconds  that  the  process   used
                     directly (in user mode), in seconds.
              W      Number  of  times  the  process  was  swapped out of main
                     memory.
              X      Average  amount  of  shared  text  in  the  process,   in
                     Kilobytes.
              Z      System's  page  size,  in  bytes.   This  is a per-system
                     constant, but varies between systems.
              c      Number  of  times  the   process   was   context-switched
                     involuntarily (because the time slice expired).
              e      Elapsed  real  (wall  clock) time used by the process, in
                     seconds.
              k      Number of signals delivered to the process.
              p      Average unshared stack size of the process, in Kilobytes.
              r      Number of socket messages received by the process.
              s      Number of socket messages sent by the process.
              t      Average resident set size of the process, in Kilobytes.
              w      Number of times that  the  program  was  context-switched
                     voluntarily,  for  instance  while  waiting  for  an  I/O
                     operation to complete.
              x      Exit status of the command.

EXAMPLES
       To run the command `wc /etc/hosts' and show the default information:
            time wc /etc/hosts

       To run the command `ls -Fs' and show just the user, system,  and  total
       time:
            time -f "\t%E real,\t%U user,\t%S sys" ls -Fs

       To  edit  the  file  BORK  and  have `time' append the elapsed time and
       number of signals to the file `log', reading the format string from the
       environment variable `TIME':
            export TIME="\t%E,\t%k" # If using bash or ksh
            setenv TIME "\t%E,\t%k" # If using csh or tcsh
            time -a -o log emacs bork

       Users of the bash shell need to use an explicit path in  order  to  run
       the external time command and not the shell builtin variant.  On system
       where time is installed in /usr/bin, the first example would become
            /usr/bin/time wc /etc/hosts

ACCURACY
       The  elapsed time is not collected atomically with the execution of the
       program; as a result, in bizarre circumstances  (if  the  time  command
       gets  stopped  or  swapped  out in between when the program being timed
       exits and when time calculates how long it took to run),  it  could  be
       much larger than the actual execution time.

       When  the  running  time  of a command is very nearly zero, some values
       (e.g., the percentage of CPU used)  may  be  reported  as  either  zero
       (which is wrong) or a question mark.

       Most  information  shown  by  time  is derived from the wait3(2) system
       call.  The numbers are only as good as those returned by wait3(2).   On
       systems   that  do  not  have  a  wait3(2)  call  that  returns  status
       information, the times(2) system call is  used  instead.   However,  it
       provides  much less information than wait3(2), so on those systems time
       reports the majority of the resources as zero.

       The `%I' and `%O' values are allegedly only `real' input and output and
       do not include those supplied  by  caching  devices.   The  meaning  of
       `real'  I/O  reported by `%I' and `%O' may be muddled for workstations,
       especially diskless ones.

DIAGNOSTICS
       The  time  command  returns  when  the  program  exits,  stops,  or  is
       terminated  by  a  signal.   If the program exited normally, the return
       value of time is the return  value  of  the  program  it  executed  and
       measured.   Otherwise,  the  return value is 128 plus the number of the
       signal which caused the program to stop or terminate.
AUTHOR
       time was written by David MacKenzie.  This man page was added  by  Dirk
       Eddelbuettel <[email protected]>, the Debian GNU/Linux maintainer, for use
       by  the  Debian  GNU/Linux  distribution  but  may of course be used by
       others.

SEE ALSO
       tcsh(1), printf(3)

                               Debian GNU/Linux                        TIME(1)