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I have a USB serial device connected to my Linux VM (Ubuntu 18.04LTS). It accepts byte streams in certain format and will return some content. To read from the device, I have written the following script:

#!/bin/sh
DATA="$1"; shift
stty -F /dev/ttyUSB0 115200 raw -echo
cat /dev/ttyUSB0 > /tmp/ttyDump.dat &
PID=$!
sleep 1s
echo -ne "$DATA" > /dev/ttyUSB0
sleep 1s
kill $PID
hexdump -ve '1/1 "%.2x"' /tmp/ttyDump.dat

If I execute line by line, I'm able to get the reply from device in ttyDump.dat. However If I run the script, the ttyDump.dat is empty.

I also tried with FD:

exec 3</dev/ttyUSB0
cat <&3 >/tmp/ttyDump.dat&

But same result.

Any clue?

Thanks!

zhangwei
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  • One thing I forgot to mention, the device also support AT commands, and the device responds to AT commands properly running from shell script, with either bash or dash shell. – zhangwei Jul 29 '19 at 09:20

1 Answers1

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Ok, I don't know why, but after I changed to use bash shell, the script works. The default shell is dash.

zhangwei
  • 21
  • Probably because echo -ne is not portable. Use printf instead. – muru Jul 29 '19 at 04:59
  • Thanks @muru for suggestion. Unfortunately I don't know what I did, but now even bash doesn't work. I also tried printf but same result. Could it be due to the device itself? One thing I forgot to mention, the device also support AT commands, and the device responds to AT commands properly running from shell script, with either bash or dash shell. – zhangwei Jul 29 '19 at 09:20