SLEEP(1)                   POSIX Programmer's Manual                  SLEEP(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       sleep -- suspend execution for an interval

SYNOPSIS
       sleep time

DESCRIPTION
       The sleep utility shall suspend execution for at least the integral
       number of seconds specified by the time operand.

OPTIONS
       None.

OPERANDS
       The following operand shall be supported:

       time      A non-negative decimal integer specifying the number of
                 seconds for which to suspend execution.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of
       sleep:

       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 messages written to standard
                 error.

       NLSPATH   Determine the location of message catalogs for the processing
                 of LC__MESSAGES.

ASYNCHRONOUS EVENTS
       If the sleep utility receives a SIGALRM signal, one of the following
       actions shall be taken:

        1. Terminate normally with a zero exit status.

        2. Effectively ignore the signal.

        3. Provide the default behavior for signals described in the
           ASYNCHRONOUS EVENTS section of Section 1.4, Utility Description
           Defaults.  This could include terminating with a non-zero exit
           status.

       The sleep utility shall take the standard action for all other signals.

STDOUT
       Not used.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

        0    The execution was successfully suspended for at least time
             seconds, or a SIGALRM signal was received. See the ASYNCHRONOUS
             EVENTS section.

       >0    An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       None.

EXAMPLES
       The sleep utility can be used to execute a command after a certain
       amount of time, as in:


           (sleep 105; command) &

       or to execute a command every so often, as in:


           while true
           do
               command
               sleep 37
           done

RATIONALE
       The exit status is allowed to be zero when sleep is interrupted by the
       SIGALRM signal because most implementations of this utility rely on the
       arrival of that signal to notify them that the requested finishing time
       has been successfully attained. Such implementations thus do not
       distinguish this situation from the successful completion case. Other
       implementations are allowed to catch the signal and go back to sleep
       until the requested time expires or to provide the normal signal
       termination procedures.

       As with all other utilities that take integral operands and do not
       specify subranges of allowed values, sleep is required by this volume
       of POSIX.1-2017 to deal with time requests of up to 2147483647 seconds.
       This may mean that some implementations have to make multiple calls to
       the delay mechanism of the underlying operating system if its argument
       range is less than this.

FUTURE DIRECTIONS
       None.

SEE ALSO
       wait

       The Base Definitions volume of POSIX.1-2017, Chapter _8, Environment
       Variables

       The System Interfaces volume of POSIX.1-2017, alarm(), sleep()

COPYRIGHT
       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                             SLEEP(1)
