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 .