Is cat the only reliable command that can read data from serial?
I have a scale that continuously send data via serial port, 2 times per second. The only reliable way on reading this data happened to be cat command. The following works:
cat /dev/ttyUSB0
But the problem with cat is that, as it doesn't receive an EOF, it continues retrieving data. I've also tried head, read and tail.
head -1 /dev/ttyUSB0 | strings
works 'almost' everytime, but now and then shows old data, and only re-running cat command fixes it (?). The string after pipe retrieves only printable data.
read line < /dev/ttyUSB0 | echo $line
now and then retrieves data, but most of the time only shows an empty line.
tail -1 < /dev/ttyUSB0
just freezes, waiting for EOF, maybe?
My issue is that i need to write a bash script that can be called and "read" /dev/ttyUSB0 and retrieve data. I'm going to use head. But I'm wondering, as cat never fails, if there's a way to capture only one line of cat output and then stop it.
Note: the port configuration is 9600 baud, 1 start bit, 8 data bits, no parity, 2 stop bits. To set the port properly this is the command:
sudo stty -F /dev/ttyUSB0 9600 -parity cs8 cstopb
command-line tty cat serial-port head
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
bumped to the homepage by Community♦ 2 days ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
add a comment |
I have a scale that continuously send data via serial port, 2 times per second. The only reliable way on reading this data happened to be cat command. The following works:
cat /dev/ttyUSB0
But the problem with cat is that, as it doesn't receive an EOF, it continues retrieving data. I've also tried head, read and tail.
head -1 /dev/ttyUSB0 | strings
works 'almost' everytime, but now and then shows old data, and only re-running cat command fixes it (?). The string after pipe retrieves only printable data.
read line < /dev/ttyUSB0 | echo $line
now and then retrieves data, but most of the time only shows an empty line.
tail -1 < /dev/ttyUSB0
just freezes, waiting for EOF, maybe?
My issue is that i need to write a bash script that can be called and "read" /dev/ttyUSB0 and retrieve data. I'm going to use head. But I'm wondering, as cat never fails, if there's a way to capture only one line of cat output and then stop it.
Note: the port configuration is 9600 baud, 1 start bit, 8 data bits, no parity, 2 stop bits. To set the port properly this is the command:
sudo stty -F /dev/ttyUSB0 9600 -parity cs8 cstopb
command-line tty cat serial-port head
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
bumped to the homepage by Community♦ 2 days ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
Did you trydd? It might work (with suitable options).
– Basile Starynkevitch
Jul 12 '17 at 16:38
Yourheadcommand may be getting slightly old data due to a buffer, and you are reading the top of it. When you triedtail, it was with other arguments. Try repeating theheadcommand options withtail
– ivanivan
Jul 12 '17 at 16:44
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Try prefixing a non-catcommand withstdbuf -i 0 -o 0, i.e.stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.
– agc
Jul 12 '17 at 19:33
add a comment |
I have a scale that continuously send data via serial port, 2 times per second. The only reliable way on reading this data happened to be cat command. The following works:
cat /dev/ttyUSB0
But the problem with cat is that, as it doesn't receive an EOF, it continues retrieving data. I've also tried head, read and tail.
head -1 /dev/ttyUSB0 | strings
works 'almost' everytime, but now and then shows old data, and only re-running cat command fixes it (?). The string after pipe retrieves only printable data.
read line < /dev/ttyUSB0 | echo $line
now and then retrieves data, but most of the time only shows an empty line.
tail -1 < /dev/ttyUSB0
just freezes, waiting for EOF, maybe?
My issue is that i need to write a bash script that can be called and "read" /dev/ttyUSB0 and retrieve data. I'm going to use head. But I'm wondering, as cat never fails, if there's a way to capture only one line of cat output and then stop it.
Note: the port configuration is 9600 baud, 1 start bit, 8 data bits, no parity, 2 stop bits. To set the port properly this is the command:
sudo stty -F /dev/ttyUSB0 9600 -parity cs8 cstopb
command-line tty cat serial-port head
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
I have a scale that continuously send data via serial port, 2 times per second. The only reliable way on reading this data happened to be cat command. The following works:
cat /dev/ttyUSB0
But the problem with cat is that, as it doesn't receive an EOF, it continues retrieving data. I've also tried head, read and tail.
head -1 /dev/ttyUSB0 | strings
works 'almost' everytime, but now and then shows old data, and only re-running cat command fixes it (?). The string after pipe retrieves only printable data.
read line < /dev/ttyUSB0 | echo $line
now and then retrieves data, but most of the time only shows an empty line.
tail -1 < /dev/ttyUSB0
just freezes, waiting for EOF, maybe?
My issue is that i need to write a bash script that can be called and "read" /dev/ttyUSB0 and retrieve data. I'm going to use head. But I'm wondering, as cat never fails, if there's a way to capture only one line of cat output and then stop it.
Note: the port configuration is 9600 baud, 1 start bit, 8 data bits, no parity, 2 stop bits. To set the port properly this is the command:
sudo stty -F /dev/ttyUSB0 9600 -parity cs8 cstopb
command-line tty cat serial-port head
command-line tty cat serial-port head
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
edited Jul 12 '17 at 21:22
Jeff Schaller
39.2k1054125
39.2k1054125
asked Jul 12 '17 at 16:14
thejavothejavo
1113
asked Jul 12 '17 at 16:14
thejavothejavo
1113
asked Jul 12 '17 at 16:14
thejavothejavo
1113
1113
bumped to the homepage by Community♦ 2 days ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
bumped to the homepage by Community♦ 2 days ago
This question has answers that may be good or bad; the system has marked it active so that they can be reviewed.
Did you trydd? It might work (with suitable options).
– Basile Starynkevitch
Jul 12 '17 at 16:38
Yourheadcommand may be getting slightly old data due to a buffer, and you are reading the top of it. When you triedtail, it was with other arguments. Try repeating theheadcommand options withtail
– ivanivan
Jul 12 '17 at 16:44
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Try prefixing a non-catcommand withstdbuf -i 0 -o 0, i.e.stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.
– agc
Jul 12 '17 at 19:33
add a comment |
Did you trydd? It might work (with suitable options).
– Basile Starynkevitch
Jul 12 '17 at 16:38
Yourheadcommand may be getting slightly old data due to a buffer, and you are reading the top of it. When you triedtail, it was with other arguments. Try repeating theheadcommand options withtail
– ivanivan
Jul 12 '17 at 16:44
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Try prefixing a non-catcommand withstdbuf -i 0 -o 0, i.e.stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.
– agc
Jul 12 '17 at 19:33
Did you try
dd ? It might work (with suitable options).– Basile Starynkevitch
Jul 12 '17 at 16:38
Did you try
dd ? It might work (with suitable options).– Basile Starynkevitch
Jul 12 '17 at 16:38
Your
head command may be getting slightly old data due to a buffer, and you are reading the top of it. When you tried tail, it was with other arguments. Try repeating the head command options with tail– ivanivan
Jul 12 '17 at 16:44
Your
head command may be getting slightly old data due to a buffer, and you are reading the top of it. When you tried tail, it was with other arguments. Try repeating the head command options with tail– ivanivan
Jul 12 '17 at 16:44
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Try prefixing a non-
cat command with stdbuf -i 0 -o 0, i.e. stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.– agc
Jul 12 '17 at 19:33
Try prefixing a non-
cat command with stdbuf -i 0 -o 0, i.e. stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.– agc
Jul 12 '17 at 19:33
add a comment |
1 Answer
1
active
oldest
votes
Your best bet is to place the tty in raw mode, and write a program that discards characters until it sees the start of a message, and then prints characters until it reaches the end of a message. With 'raw' added to the stty, fgetc() can be used on the tty to get a single character.
off the cuff psuedo:
char = fgetc(serial_port);
if char == START_CHARACTER {
putc(char);
for (i=0;i<MESSAGE_LENGTH;i++){
putc(fgetc(serial_port));
}
}
It may also be possible to do this with sed and a raw tty, see this other question:
https://stackoverflow.com/questions/20943025/how-can-i-get-sed-to-quit-after-the-first-matching-address-range
edited Aug 28 '18 at 8:04
chaos
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Your best bet is to place the tty in raw mode, and write a program that discards characters until it sees the start of a message, and then prints characters until it reaches the end of a message. With 'raw' added to the stty, fgetc() can be used on the tty to get a single character.
off the cuff psuedo:
char = fgetc(serial_port);
if char == START_CHARACTER {
putc(char);
for (i=0;i<MESSAGE_LENGTH;i++){
putc(fgetc(serial_port));
}
}
It may also be possible to do this with sed and a raw tty, see this other question:
https://stackoverflow.com/questions/20943025/how-can-i-get-sed-to-quit-after-the-first-matching-address-range
edited Aug 28 '18 at 8:04
chaos
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
add a comment |
Your best bet is to place the tty in raw mode, and write a program that discards characters until it sees the start of a message, and then prints characters until it reaches the end of a message. With 'raw' added to the stty, fgetc() can be used on the tty to get a single character.
off the cuff psuedo:
char = fgetc(serial_port);
if char == START_CHARACTER {
putc(char);
for (i=0;i<MESSAGE_LENGTH;i++){
putc(fgetc(serial_port));
}
}
It may also be possible to do this with sed and a raw tty, see this other question:
https://stackoverflow.com/questions/20943025/how-can-i-get-sed-to-quit-after-the-first-matching-address-range
edited Aug 28 '18 at 8:04
chaos
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
add a comment |
Your best bet is to place the tty in raw mode, and write a program that discards characters until it sees the start of a message, and then prints characters until it reaches the end of a message. With 'raw' added to the stty, fgetc() can be used on the tty to get a single character.
off the cuff psuedo:
char = fgetc(serial_port);
if char == START_CHARACTER {
putc(char);
for (i=0;i<MESSAGE_LENGTH;i++){
putc(fgetc(serial_port));
}
}
It may also be possible to do this with sed and a raw tty, see this other question:
https://stackoverflow.com/questions/20943025/how-can-i-get-sed-to-quit-after-the-first-matching-address-range
edited Aug 28 '18 at 8:04
chaos
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
Your best bet is to place the tty in raw mode, and write a program that discards characters until it sees the start of a message, and then prints characters until it reaches the end of a message. With 'raw' added to the stty, fgetc() can be used on the tty to get a single character.
off the cuff psuedo:
char = fgetc(serial_port);
if char == START_CHARACTER {
putc(char);
for (i=0;i<MESSAGE_LENGTH;i++){
putc(fgetc(serial_port));
}
}
It may also be possible to do this with sed and a raw tty, see this other question:
https://stackoverflow.com/questions/20943025/how-can-i-get-sed-to-quit-after-the-first-matching-address-range
edited Aug 28 '18 at 8:04
chaos
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
edited Aug 28 '18 at 8:04
chaos
35.1k773116
edited Aug 28 '18 at 8:04
chaos
35.1k773116
edited Aug 28 '18 at 8:04
chaos
35.1k773116
35.1k773116
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
answered Jul 12 '17 at 20:40
KJ4IPSKJ4IPS
1643
1643
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
add a comment |
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
thanks you very much KJ4IPS!, i'll try not to "sound" rude, but I lack the vocabulary to "sound polite enough", so excuse me. But the answer you've wrote doesn't solve my problem. The scale already transmits data with 2Hz frequency. Inmediately after been turned on. Constantly. It never stops. So it's not possible to reach an end of message. On the other hand, I'm interested in solving this with pure bash.
– thejavo
Jul 14 '17 at 12:48
add a comment |
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Did you try
dd? It might work (with suitable options).– Basile Starynkevitch
Jul 12 '17 at 16:38
Your
headcommand may be getting slightly old data due to a buffer, and you are reading the top of it. When you triedtail, it was with other arguments. Try repeating theheadcommand options withtail– ivanivan
Jul 12 '17 at 16:44
Thank Basile, I'll investigate dd. Ivan, I agree with you. I've assumed that I'm reading some kind of buffer of stdout. ¿is there a way to reset it?. And don't understand why cat isn't affected with this buffer issue. Thank you. I've used head -10 /dev/ttyUSB0 | tail -1. But get the same result, erratic.
– thejavo
Jul 12 '17 at 17:31
Try prefixing a non-
catcommand withstdbuf -i 0 -o 0, i.e.stdbuf -i 0 -o 0 head -1 /dev/ttyUSB0 | strings.– agc
Jul 12 '17 at 19:33