Until Command in Linux: Create Loops Until Condition is True

The until command in Linux is the opposite of the while command, but it executes something while the test is false, or with non-zero values.

Its syntax is:

until [CONDIÇÃO]do  [COMANDOS]done

Example:

#!/bin/bashcounter=0until [ $counter -gt 3 ]do  echo Counter: $counter  ((counter++))done

When executed:

$ ./contador Counter: 0Counter: 1Counter: 2Counter: 3

The until is useful for making a script wait until a command no longer returns an error, since it only executes if the test return is different from zero.

A zero exit code from a program usually indicates that it executed successfully.

In this example, the until command is used to wait until the host can ping the IP 8.8.8.8. When the ping command successfully pings the host 8.8.8.8, it will return zero, causing the processing to exit the loop:

#!/bin/bashuntil ping -c 1 8.8.8.8 &>/dev/nulldo    echo "Esperando a rede..."    sleep 1doneecho "A rede está no ar"

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