The sleep command makes your Linux computer do nothing. Counter-intuitive perhaps, but a period of inactivity is sometimes just what’s needed. This article shows you how to use this Bash shell command effectively.
sleep is easy. On the command line type
sleep, a space, a number, and then press Enter.
The cursor will disappear for five seconds and then return. What happened? Using
sleep on the command line instructs Bash to suspend processing for the duration you provided. In our example this was five seconds.
We can pass durations to
sleep in days, hours, and minutes, as well as in seconds. To do this include a suffix of either
d, h, m, or
s with the duration. To cause sleep to pause for one day, four hours, seven minutes and five seconds, use a command like this:
sleep 1d 4h 7m 5s
s suffix (for seconds) is optional. With no suffix,
sleep will treat any duration as seconds. Suppose you wanted to have
sleep pause for five minutes and twenty seconds. One correct format of this command is:
sleep 5m 20
If you forget to provide the
m suffix on the minutes duration, you will instruct
sleep to pause for five seconds and then again for twenty seconds. So
sleep will pause for 25 seconds.
Many commands require you to provide parameters in a specific order, but
sleep is very forgiving. You can provide them in any order and
sleep will make sense out of them. You can also provide a floating point number as a parameter. For example, 0.5h is a valid way to indicate you wish
sleep to pause for half an hour.
All of the following (increasingly eccentric) commands tell
sleep to pause for 10 seconds.
sleep 5 5s
Sleep 1 1 1s 1 1 1s 1 2
Using Sleep to Pause Before a Command
sleep command can be used to give a pause before the execution of a command. This command would pause for 15 seconds and then give a bleep.
sleep 15 && echo -en '\007'
Using Sleep to Pause Between Two Commands
You can use
sleep to give a pause between two commands. This command would list the files in your Documents directory, pause for five seconds and then change the current working directory to your home directory:
ls -R ~/Documents && sleep 5 && cd ~
Using Sleep to Pause Execution of a Script
You can use the
sleep command in shell scripts to pause execution of the script for a precise amount of time. Typically, you’d do this to allow some process sufficient time to complete before the script continues its processing. You can also use it to rate-limit the requests a script makes to another resource.
To demonstrate exactly that, here is a script that calls out to a Google web service using
curl. When you query the web service with the ISBN number of a book, it responds with a dump of JSON data regarding that book. We can parse that data by passing it through the
jq utility to retrieve the title of the book. So that the script doesn’t stress the web service, it sleeps for one second between web requests.
Create a file containing the following text, and save it as
#!/bin/bash for book in `cat $1` do echo $book":" curl -s https://www.googleapis.com/books/v1/volumes?q=isbn:$book | jq '.items | . | .volumeInfo.title' echo "" sleep 1 done echo "All done."
Type the following command to set the execution permissions and make the script executable.
chmod +x check_book.sh
The script requires the
jq utilities. Use
apt-get to install these packages onto your system if you’re using Ubuntu or another Debian-based distribution. On other Linux distributions, use your Linux distribution’s package management tool instead.
sudo apt-get install curl
sudo apt-get install jq
Create a text file containing the following numbers, and save it as
9781565921276 9781874416685 9781565921672 9780521431088 9781491941591
check_book.sh script and pass in the
books.txt file as a parameter.
The requests are made to the Google web service at one second intervals. The title of the book will appear shortly after each ISBN number is queried.
That’s all there is to
sleep. The inner workings of the
check_book.sh script are beyond the scope of this article. The script was chosen purely to illustrate a valid use of the
sleep command. If you wish to read more about the two main components of the script, refer to the
curl project page and the
jq on-line manual.