Stupid Bash Tricks: Simple Loop With Timestamp
We ran into an interesting situation where we needed to know two things: whether or not a particular server was down, and when, exactly, it went down. We had requested some service be done on the server, and had a shell open via ssh. A simple solution that did the trick, and illustrates some stupid BASH tricks, is this script:
u-1@srv-1 u-1 $ until [ 6 -eq 9 ]
> do
> echo $(date)
> sleep 1
> done
Mon Mar 17 14:01:13 PST 2003
Mon Mar 17 14:01:14 PST 2003
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The time increments once every second by utilizing the sleep command. Since 6 hasn't yet turned out to be a 9 (to our knowledge), this script most likely will loop forever. If you don't use sleep, you'll waste a lot of CPU power. This can be entered in one line:
until [ 6 -eq 9 ]; do echo $(date); sleep 1; done
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Another application of this is to test serial ports. We have a cheap breakout box that has tri-state LEDs, as most breakout boxes do. By running this simple script:
until [ 6 -eq 9 ]; do echo thequickbrownfox > /dev/ttyS0; done
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We can tell which line is transmitting data:
The light on pin 2 is orange. If you just hook up the breakout box without the
program, the light is red. Pushing a key doesn't help, because the light blinks too fast.
For other stupid BASH tricks, click here.
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