Bash script: Pause script before proceeding

Normally, a Bash script will execute each line of code the moment it reaches it, then immediately move on to the next. But it is also possible to add pauses to a Bash script in order to delay it or allow the user time to respond to a prompt, etc.

In this tutorial, you will learn how to add pauses to a Bash script on a Linux system. Check out our examples below to see how pauses can be facilitated by the read or sleep command, and how this functionality has practical use in some scripts.

In this tutorial you will learn:

• How to pause Bash script with sleep
• How to pause Bash script with read
• How to make a prompt that has a timer in Bash scripting

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	Any Linux distro
Software	Bash shell (installed by default)
Other	Privileged access to your Linux system as root or via the sudo command.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

Bash script examples: Pause script before proceeding

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1. Let’s start with a basic example of the sleep command. This is easy to use, and allows us to pause our Bash script for any amount of time in seconds, minutes, hours, or even days.

   #!/bin/bash
   
   echo "Script will proceed in 5 seconds..."
   
   sleep 5s
   
   echo "Thanks for waiting."

   Obviously this script does not have much practicality, but you can see how the sleep command works. You can also use decimals with sleep and other units of time as mentioned above. Note you do not need to include the s for seconds, it is optional.

   sleep 10 # pauses for 10 seconds
   sleep 5.5 # pauses for 5.5 seconds
   sleep 10m # pauses for 10 minutes
   sleep 3h # pauses for 3 hours
   sleep 3.5h # pauses for 3 hours, 30 minutes
   sleep 2d # pauses for 2 days
   

2. The example above shows us how the sleep command works, but how would it be useful in a real Bash script? Pausing a script proves very useful in loops, specifically. Loops tend to execute very quickly at times, and can overwhelm your system’s resources if you do not employ a sleep command or similar to force the loop to take a break.

   #!/bin/bash
   
   var=0
   
   while [ $var -lt 4 ]
   do
   	ssh user@10.0.0.1
   	sleep 1m
   	((var++))
   done

   The script above will continuously try to establish an SSH connection with a host, up to five times. This is a nice way to try and get a connection to a computer which is in the process of coming online, and you do not want to keep entering the SSH command yourself. The sleep command in our script prevents the while loop from spamming the ssh command, by forcing it to pause for one minute. This is just one example of how pausing your script with the sleep command can be very handy.

3. We can also use the read command to pause our Bash script. Use the -t command and the number of seconds to pause the script. We are also including the -p option and some informative text in this example, but it is not strictly necessary.

   #!/bin/bash
   
   read -p "Pausing for 5 seconds" -t 5
   
   echo "Thanks for waiting."

   This method is nice because, to skip the timer, you can simply press Enter on your keyboard to force the timer to expire and have the script proceed. Returning to our SSH script in the previous example, imagine if we had used the read command instead of sleep, so that we could force a new SSH attempt if we got impatient for the while loop to be triggered again.

4. Since the read command is normally used to read input from the command line, the -t option allows us to make our user prompt expire after a certain time. Let’s look at a practical example.

   #!/bin/bash
   
   read -p "Do you want to proceed? (yes/no) " -t 10 yn
   
   if [ -z "$yn" ]
   then
         echo -e "\nerror: no response detected"
         exit 1
   fi
   
   case $yn in 
   	yes ) echo ok, we will proceed;;
   	no ) echo exiting...;
   		exit;;
   	* ) echo invalid response;
   		exit 1;;
   esac
   
   echo doing stuff...

   The script above is a simple yes or no prompt. These are very common throughout Linux and Bash scripts, which usually ask a user if they would like to proceed with something. In the script above, our -t 10 option in the read command will make the script proceed after 10 seconds, unless the user enters a response before then. Our if statement is triggered if an empty response is detected, and will issue an error and exit. If a response is detected, then the case statement is triggered.

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Closing Thoughts

In this tutorial, you saw how to pause a Bash script before proceeding. We tried to stay away from silly examples in the tutorial, and only show practical scripts that have a useful application in the real world. The goal was to allow you to see how a sleep pause and a read pause can both be useful in different situations.