The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


time - time a simple command


time [-p] utility [argument...]


The time utility invokes the utility named by the utility operand with arguments supplied as the argument operands and writes a message to standard error that lists timing statistics for the utility. The message includes the following information:

The precision of the timing will be no less than the granularity defined for the size of the clock tick unit on the system, but the results will 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 Compound 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)


The time utility supports the XBD specification, Utility Syntax Guidelines  .

The following option is supported:

Write the timing output to standard error in the format shown in the STDERR section.


The following operands are supported:
The name of a utility that is to be invoked. If the utility operand names any of the special built-in utilities in Special Built-in Utilities , the results are undefined.
Any string to be supplied as an argument when invoking the utility named by the utility operand.


Not used.




The following environment variables affect the execution of time:
Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
If set to a non-empty string value, override the values of all the other internationalisation variables.
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single- 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.
Determine the location of message catalogues for the processing of LC_MESSAGES .
Determine the search path that will be used to locate the utility to be invoked. See the XBD specification, Environment Variables  .




Not used.


The standard error will be used to write the timing statistics. If -p is specified, the following format will be used in the POSIX locale:

"real %f\nuser %f\nsys %f\n", <real seconds>, <user seconds>, <system seconds>

where each floating-point number is expressed in seconds. The precision used may be less than the default six digits of %f, but will 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 follow the radix character). The number of digits following the radix character will 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.






If the utility utility is invoked, the exit status of time will be the exit status of utility; otherwise, the time utility will exit with one of the following values: The following exit values are returned:
An error occurred in the time utility.
The utility specified by utility was found but could not be invoked.
The utility specified by utility could not be found.




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.


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'




sh times special built-in utility.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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