sleep man page

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.

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.

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.

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.1‐2008, 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.

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.

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.1‐2008 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.

See Also

wait

The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables

The System Interfaces volume of POSIX.1‐2008, alarm(), sleep()

Info

2013 IEEE/The Open Group POSIX Programmer's Manual