Loops are one of the fundamental concepts of programming languages. Loops are handy when you want to run a series of commands over and over again until a specific condition is met.
This tutorial explains the basics of the
until loop in Bash.
until loop is used to execute a given set of commands as long as the given condition evaluates to false.
until loop takes the following form:
until [CONDITION] do [COMMANDS] done
The condition is evaluated before executing the commands. If the condition evaluates to false, commands are executed. Otherwise, if the condition evaluates to true the loop will be terminated and the program control will be passed to the command that follows.
In the example below, on each iteration the loop prints the current value of the variable
counter and increments the variable by one.
#!/bin/bash counter=0 until [ $counter -gt 5 ] do echo Counter: $counter ((counter++)) done
The loop iterates as long as the
counter variable has a value greater than four. The script will produce the following output:
Counter: 0 Counter: 1 Counter: 2 Counter: 3 Counter: 4 Counter: 5
continue statements to control the loop execution.
until Loop Example
The following script may be useful when your git host has downtime, and instead of manually typing
git pull multiple times until the host is online, you can run the script once. It will try to pull the repository until it is successful.
#!/bin/bash until git pull &> /dev/null do echo "Waiting for the git host ..." sleep 1 done echo -e "\nThe git repository is pulled."
The script will print “Waiting for the git host …” and
sleep for one second until the git host goes online. Once the repository is pulled, it will print “The git repository is pulled.".
Waiting for the git host ... Waiting for the git host ... Waiting for the git host ... The git repository is pulled.
until loops are similar to each other. The main difference is that the
while loop iterates as long as the condition evaluates to
true and the
until loop iterates as long as the condition evaluates to
If you have any questions or feedback, feel free to leave a comment.