Run command every second in Bash?

Question

I want to write some image downloader and assign it on bash. What I have and what I need:

I have:

1. Command, which works fine (something like wget

Answer 1

To add my two cents to this... If the cron's one minute interval is too long for you, you can take advantage of the systemd's capability to restart services repeatedly.

[Unit]
Description=Poll something each second

[Service]
Type=simple
ExecStart=/opt/poller/poll.sh
Restart=always
RestartSec=1
StartLimitInterval=0

[Install]
WantedBy=multi-user.target

I know it's a messy and sort of "never ever do this" approach. But it works perfectly an is fairly simple to set up.

Answer 2

If you want to run a command at one second intervals (one second between the end of one command and the beginning of the next, which is not the same as running every second), just do:

while sleep 1; do cmd; done

If you want that to start on reboot, the method will depend on your system.

Answer 3

The command watch will do this for you straight up. It also displays the result in a nice way.

$ watch -n 1 date

Substitute date for your command. The -n option specifies the interval in seconds.