CODEWITHSUNDEEP
linuxbashserial-porthexnon-ascii-characters
Peter von Frosta
Peter von Frosta

Reputation: 75

how to send asci and non asci character over serial port from bash (script)

I try to send some hex values (mixed with asci chars).

what i like to have: send_string = {0x2d, 0x2e, 0x01,..., "Hallo"}

what i am able to get: send_string= "0x2d0x2e0x10...Hallo"

Script:

#!/bin/bash

#USB device path
USBDEV=/dev/ttyUSB0


#disable DTR
stty -F $USBDEV -hupcl
#set baud
stty -F $USBDEV 9600

pattern1=0x2d
pattern2=0x2e
adr=0x01
cmd=0x21

nl=0x0a
end=0x00

txt1="Hallo"
txt2="Bye"

string=$(echo ${pattern1}${pattern2}${adr}${cmd}"test"${nl}"haha"${end})
#string=$(echo \0x2e\0x2d\0x01\0x21"test"\0x0a"haha"\0x00)

echo $string
echo $string >> $USBDEV

exit 0

Output

0x2d0x2e0x010x21test0x0ahaha0x00

Problem

The hex values of vars pattern1, pattern2, adr, ... should be stored in the string as not ASCI charackters.

If the string would be prepered as i need to, the output must have non asci characters. But it has not.

i tried some ways but all gained confusion only.

Upvotes: 0

Views: 827

Answers (2)

chepner
chepner

Reputation: 532448

I recommend using printf directly for binary data; you can't store arbitrary binary data (namely, a null byte) in a shell variable.

#!/bin/bash

#USB device path
USBDEV=/dev/ttyUSB0


#disable DTR
stty -F $USBDEV -hupcl
#set baud
stty -F $USBDEV 9600

printf '.-\001!%s\n%s\000' "$txt1" "$txt2" > "$USBDEV"

exit 0

Upvotes: 0

choroba
choroba

Reputation: 242383

You can use the $'' special quotes.

pattern1=$'\x2d'

This doesn't work for \x00, though. The only possible way to print it I know is

printf '\x00'

but you can't assign it to a variable. You need to switch to a more advanced scripting language to be able to do it. For example, in Perl

$end = "\x00";

works fine.

Upvotes: 1

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