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Top Forums Shell Programming and Scripting Read line from serial device with BASH Post 302985016 by Don Cragun on Thursday 3rd of November 2016 03:52:55 PM
Old 11-03-2016
You might also want to consider using:
Code:
printf 'add read 0\n\r'

instead of:
Code:
echo "add read 0" > /dev/ttyACM0
echo -e '\r' > /dev/ttyACM0

Note that the two echo commands each open and close the device and each prints a <newline> character that might neither be needed nor desirable from the second echo.

Alternatively, you might want to consider opening the device once at the start of your script using exec to open (and hold open) your device:
Code:
exec <> /dev/ttyACM0

(replacing standard input for the entire script in this case, but a different file descriptor can also be specified if some other file is being fed into your script). Then you could consider using the stty utility to set appropriate parameters for your device such as icrnl or -icrnl and igncr or -igncr (depending on whether your device sends <carriage-return> and/or <newline> characters as line terminators when you read data from your device) and ocrnl or -ocrnl, onlcr or -onlcr, and onocr or -onocr depending on what it wants to see as line terminators in commands it receives from your script. (And, of course, check the stty man page on your system for other operands that might simplify using your device.)
 

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STTY(1) 						      General Commands Manual							   STTY(1)

NAME
stty - set terminal parameters SYNOPSIS
stty [-ag] stty encoded-form stty speed ispeed speed ospeed speed cs5 cs6 cs7 cs8 [-]parenb [-]parodd [-]hupcl [-]cstopb [-]cread [-]clocal [-]ignbrk [-]brkint [-]ign- par [-]parmrk [-]inpck [-]istrip [-]inlcr [-]igncr [-]icrnl [-]ixon [-]ixoff [-]ixany [-]opost [-]onlcr [-]xtabs [-]onoeot [-]isig [-]icanon [-]iexten [-]echo [-]echoe [-]echok [-]echonl [-]noflsh [-]lflusho eof=c eol=c erase=c erase=c intr=c kill=c quit=c susp=c start=c stop=c rprnt=c lnext=c flush=c min=n time=n rows n cols n cooked raw [-]evenp [-]parity [-]oddp [-]nl ek sane DESCRIPTION
Stty shows or changes the parameters of the terminal connected to standard input. Stty takes a myriad of arguments most of which are mapped directly to the flags and special characters described in tty(4), so we won't describe them here. Stty has three forms of operation. First, without any arguments stty shows all terminal attributes that are different from the default state. Option -a makes stty print all terminal attributes, and -g lets stty print the attributes in a special encoded form, a simple row of colon separated hexadecimal numbers. In the second form of operation stty takes an encoded form as produced by the -g option and sets the terminals attributes to its decoded value. In the third form stty interprets a series of flags and parameters settings and modifies the terminal attributes accordingly. Flags can be given as icanon or -icanon for instance, either setting or clearing the ICANON flag. Special character values can by set like intr=^C for example, which sets the interrupt character to CTRL-C. You can either use a real CTRL-C, or the two characters `^' and `C'. In any case it is probably necessary to use quotes to guard it from the shell: intr='^C'. A number alone is interpreted as a baud rate setting for both the input and output rate. The input or the output rate can be set sepa- rately with use of the ispeed and ospeed prefixes to the number. The character size can be set with cs5, cs6, cs7 or cs8. The MIN and TIME value, and the number of rows and columns of the window can also be set using one of the keywords min, time, rows or cols, followed by a decimal number that is the value of the setting. Stty accepts several keywords that are not named by corresponding flags or parameters in tty(4). They set several attributes at once: cooked Same as icrnl ixon opost onlcr isig icanon iexten echo, setting all the attributes that are needed for line oriented mode. raw Same as -icrnl -ixon -opost -onlcr -isig -icanon -iexten -echo, setting all the attributes for a raw data channel. evenp parity These synonyms are equal to cs7 parenb -parodd, setting the line to 7 bits even parity. oddp Same as cs7 parenb parodd, setting the line to 7 bits odd parity. -parity -evenp -oddp All synonyms for cs8 -parenb, setting the line to 8 bits, no parity. nl Same as icrnl, setting carriage return to line feed input translation. -nl Same as -icrnl -inlcr -igncr, disabling any carriage return or line feed handling. ek Set the ERASE and KILL special characters back to the default. sane Set all attributes to the default except things like the line speed and parity, because their "sane" value is probably what it is right now. The default values are compiled into stty from the <termios.h> include file. Use stty sane; stty -a to know what they are. FILES
/etc/ttytab The init field of this file may contain an stty command to set the attributes to match an attached RS232 terminal or modem. SEE ALSO
tty(4), ttytab(5). NOTES
The cooked, raw, rows and cols keywords are Minix additions beyond the keywords defined by POSIX. Rows and cols are common UNIX exten- sions, however. There are more Minix specific flags that match the Minix specific attributes described in tty(4). AUTHOR
Kees J. Bot (kjb@cs.vu.nl) STTY(1)
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