Do task until it succeeds

A story

I was working on my vm and needed to reboot it. In order to ssh back into the machine, I would have to wait for it to come back online and start up ssh.

Instead of manually polling myself, I whipped up this little one-liner:

while ! ssh centos7-01a; do true; done

So it failed silently at first, and then started showing ssh_exchange_identification: Connection closed by remote host.
Then when OpenSSH was finally ready for me, my kerberos authentication proceeded normally and I was in.
Upon closing my session, the while loop concluded and returned me to my shell.

I came up with this little snippet on a whim, and it actually helped me out and was not obtrusive and did not fail in any way.

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An improvement upon while true loop

The story

So normally when I want to see output for something, I’ll run a while true loop.

while true; do zabbix_get -s rhevtester.example.com -k 'task.converter_cpu'; done

That doesn’t always stop even when I mash ^C (CTRL+C).

The solution

So I offer my improvement. The way to stop the loop is obvious, and also I will explain it.

while test ! -f /tmp/foo; do zabbix_get -s rhevtester.example.com -k 'task.converter_cpu'; done

To stop the loop, in another shell just:

touch /tmp/foo