sleep - suspend execution for an interval
The sleep utility shall suspend execution for at least the integral number of seconds specified by the time operand.
The following operand shall be supported:
- A non-negative decimal integer specifying the number of seconds for which to suspend execution.
The following environment variables shall affect the execution of sleep:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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).
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
If the sleep utility receives a SIGALRM signal, one of the following actions shall be taken:
Terminate normally with a zero exit status.
Effectively ignore the signal.
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.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- The execution was successfully suspended for at least time seconds, or a SIGALRM signal was received. See the ASYNCHRONOUS EVENTS section.
- An error occurred.
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
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.1-2008 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.
XBD Environment Variables
XSH alarm, sleep
First released in Issue 2.
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