Syntax for a single-line while loop in Bash

Brian_Deacon_409 0
Viewed 881222

I am having trouble coming up with the right combination of semicolons and/or braces. I'd like to do this, but as a one-liner from the command line:

while [ 1 ]
do
    foo
    sleep 2
done
while-loop loops bash
14 Answers

Using while: 

while true; do echo 'while'; sleep 2s; done

Using for Loop:

for ((;;)); do echo 'forloop'; sleep 2; done

Using Recursion, (a little bit different than above, keyboard interrupt won't stop it) 

list(){ echo 'recursion'; sleep 2; list; } && list;
user_13345610

I like to use the semicolons only for the WHILE statement, and the && operator to make the loop do more than one thing...

So I always do it like this

while true ; do echo Launching Spaceship into orbit && sleep 5s && /usr/bin/launch-mechanism && echo Launching in T-5 && sleep 1s && echo T-4 && sleep 1s && echo T-3 && sleep 1s && echo T-2 && sleep 1s && echo T-1 && sleep 1s && echo liftoff ; done
user_5948800

You don't even need to use do and done. For infinite loops I find it more readable to use for with curly brackets. For example:

for ((;;)) { date ; sleep 1 ; }

This works in bash and zsh. Doesn't work in sh.

user_27538510

You can also put that loop in the background (e.g. when you need to disconnect from a remote machine)

nohup bash -c "while true; do aws s3 sync xml s3://bucket-name/xml --profile=s3-profile-name; sleep 3600; done &"
user_43137350
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