Linux command
until 命令
文本
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常用示例
Loop until condition
until [condition]; do [commands]; done
Wait for file
until [ -f [file] ]; do sleep 1; done
Wait for process
until pgrep [process]; do sleep 1; done
Counter loop
until [ $i -gt 10 ]; do echo $i; i=$((i+1)); done
说明
until is a shell loop construct that repeatedly executes a block of commands as long as a condition evaluates to false (non-zero exit status). It is the logical opposite of while, which loops while a condition is true. The condition is tested before each iteration, so if it is already true when the loop starts, the body never executes. The most common use of until is polling for a condition to become true, such as waiting for a network host to come online, a file to appear, or a process to start. Combined with sleep, it provides a simple way to implement retry logic in shell scripts. The exit status of an until loop is the exit status of the last command executed in the body. If the body never executes because the condition is already true, the exit status is zero.
FAQ
What is the until command used for?
until is a shell loop construct that repeatedly executes a block of commands as long as a condition evaluates to false (non-zero exit status). It is the logical opposite of while, which loops while a condition is true. The condition is tested before each iteration, so if it is already true when the loop starts, the body never executes. The most common use of until is polling for a condition to become true, such as waiting for a network host to come online, a file to appear, or a process to start. Combined with sleep, it provides a simple way to implement retry logic in shell scripts. The exit status of an until loop is the exit status of the last command executed in the body. If the body never executes because the condition is already true, the exit status is zero.
How do I run a basic until example?
Run `until [condition]; do [commands]; done` in a terminal, then adjust file names, paths, flags, or remote targets for your system.
Where can I find more until examples?
This page includes 4 examples for until, plus related commands for nearby Linux tasks.