reading from serial using shellscript - shell

Question

I have a serial port device that I would like to test using Linux command line.
And if I run the following command from terminal, it gives output
cat < /dev/ttyS0 &
This command opens the serial port and relays what it reads from it to its stdout.So, I tried it from shell script file but it is not working
fName="test.txt";
awk '
BEGIN { RS = "" ; FS = "\n" }
{
address = '/dev/ttyS0';
system("cat < " address );
}
END {
}' "$fName";
But it is not working and giving output.How can I listen to communication between a process and a serial port? Thanks

Answer 1

Using awk timeouts
I've successfully read something under dash, be using GAWK_READ_TIMEOUT environment variable:
out=`GAWK_READ_TIMEOUT=3000 awk '{print}' </dev/ttyS0 & sleep 1 ; echo foo >/dev/ttyS0`
On my terminal, this output:
echo "$out"
foo
Password:
or
echo "$out"
Login incorrect
testhost login:
Using bash timeouts
You could use FD under bash as:
exec 5>/dev/ttyS0
exec 6</dev/ttyS0
while read -t .1 -u 6 line;do
echo $line
done
or, to read unfinished lines:
while IFS= read -d '' -t .1 -u 6 -rn 1 char;do
echo -n "$char"
done
echo
So you could:
echo 'root' >&5
while IFS= read -d '' -t .1 -u 6 -rn 1 char;do
echo -n "$char"
done
echo 'password is 1234' >&5
while IFS= read -d '' -t .1 -u 6 -rn 1 char;do
echo -n "$char"
done
... Once done, you could close FD by running:
exec 6<&-
exec 5>&-
Sample bash poor terminal script
I've logged and test some commands with:
#!/bin/bash
exec 5>/dev/ttyS0
exec 6</dev/ttyS0
readbuf() {
while IFS= read -d '' -t .1 -u 6 -rn 1 char;do
echo -n "$char"
done
};
while [ "$cmd" != "tquit" ] ;do
readbuf
read cmd
echo >&5 "$cmd"
done