PROLOG

       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

       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(1POSIX)