Sleep (command)

In computing, sleep is a command in Unix, Unix-like and other operating systems that suspends program execution for a specified time.

Overview
The sleep instruction suspends the calling process for at least the specified number of seconds (the default), minutes, hours or days.

sleep for Unix-like systems is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX and the Single Unix Specification. It first appeared in Version 4 Unix.

The version of  bundled in GNU coreutils was written by Jim Meyering and Paul Eggert. The command is also available in the OS-9 shell, in the KolibriOS Shell, and part of the FreeDOS Package group Utilities. The FreeDOS version was developed by Trane Francks and is licensed under the GPL.

A  command is also part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.

In PowerShell,  is a predefined command alias for the   cmdlet which serves the same purpose. Microsoft also provides a  resource kit tool for Windows which can be used in batch files or the command prompt to pause the execution and wait for some time. Another native version is the  command which is part of current versions of Windows.

The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities. The sleep command has also been ported to the IBM i operating system.

Usage
Where number is an integer number to indicate the time period in seconds. Some implementations support floating point numbers.

Options
None.

Examples
Causes the current terminal session to wait 30 seconds.

Causes the current terminal session to wait 5 hours

GNU sleep
Wait 3 hours then play the file foo.mp3

Note that  and   are illegal since sleep takes only one value and unit as argument. However,  (a floating point ) is allowed. Consecutive executions of sleep can also be used.

Sleep 5 hours, then sleep another 30 minutes.

The GNU Project's implementation of sleep (part of coreutils) allows the user to pass an arbitrary floating point or multiple arguments, therefore   (a space separating hours and minutes is needed) will work on any system which uses GNU sleep, including Linux.

Possible uses for  include scheduling tasks and delaying execution to allow a process to start, or waiting until a shared network connection most likely has few users to wget a large file.