Syntax for a single-line Bash infinite while loop

Question

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 [         


        

Answer 1

If you want the while loop to stop after some condition, and your foo command returns non-zero when this condition is met then you can get the loop to break like this:

while foo; do echo 'sleeping...'; sleep 5; done;

For example, if the foo command is deleting things in batches, and it returns 1 when there is nothing left to delete.

This works well if you have a custom script that needs to run a command many times until some condition. You write the script to exit with 1 when the condition is met and exit with 0 when it should be run again.

For example, say you have a python script batch_update.py which updates 100 rows in a database and returns 0 if there are more to update and 1 if there are no more. The the following command will allow you to update rows 100 at a time with sleeping for 5 seconds between updates:

while batch_update.py; do echo 'sleeping...'; sleep 5; done;

Answer 2

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;

Answer 3

A very simple infinite loop.. :)

while true ; do continue ; done

Fr your question it would be:

while true; do foo ; sleep 2 ; done

Answer 4

while true; do foo; sleep 2; done

By the way, if you type it as a multiline (as you are showing) at the command prompt and then call the history with arrow up, you will get it on a single line, correctly punctuated.

$ while true
> do
>    echo "hello"
>    sleep 2
> done
hello
hello
hello
^C
$ <arrow up> while true; do    echo "hello";    sleep 2; done

Answer 5

Colon is always "true":

while :; do foo; sleep 2; done

Answer 6

It's also possible to use sleep command in while's condition. Making one-liner looking more clean imho.

while sleep 2; do echo thinking; done