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
IEEE Std 1003.1-2001, 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 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 IEEE Std 1003.1-2001 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 System Interfaces volume of IEEE Std 1003.1-2001, alarm(),
sleep()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .