How to get the results from "\033[6n" in an sh script

Question

It took me 10 hours of searching the net, and testing techniques to get the results that worked on any shell (#!/bin/sh).

In BASH this is relatively simple, because read can be told how many characters are to be grabbed, and if a delimiter is found it will not wait to exit.

stty -icanon -echo; echo -en "\033[6n"; read -d R -n 12 ESCPOS; stty "$x_TERM"; \
ESCPOS=`echo "$ESCPOS" | tail -c +3`; echo "$ESCPOS"

How to write a sh script version, compatible with any shell?

Answer 1

Copied from https://unix.stackexchange.com/a/88327

Assuming your /bin/sh is a POSIX sh (on Solaris 10 and older which had a Bourne shell there instead, use /usr/xpg4/bin/sh instead):

if [ -t 0 ] && [ -t 1 ]; then
  old_settings=$(stty -g) || exit
  stty -icanon -echo min 0 time 3 || exit
  printf '\033[6n'
  pos=$(dd count=1 2> /dev/null)
  pos=${pos%R*}
  pos=${pos##*\[}
  x=${pos##*;} y=${pos%%;*}
  stty "$old_settings"
fi

That assumes the whole response will come in one go waiting for it for up to 0.3 seconds. That should be generally true for terminal emulators and pty devices, but not necessarily for terminals over serial. You could change it to min 8 time 3 to keep waiting (up to 0.3 second between each byte) until 8 bytes have been read, but with the drawback that it will take always at least 0.3 seconds if the answer is shorter than 8 bytes and would hang forever if there's no answer).

You could use awk -F'[^0-9]+' -v RS=R '{print $3, $2; exit}' with min 1 time 0. That would work with awk implementations other than mawk (which insists in accumulating a buffer full of data on input before starting to process it).

In the end, reading one byte at a time like you do in your own answer is the most reliable. You may want to add a timeout to account for terminals that don't send a response.

Answer 2

Note:

unlike the wrongly copied and continually upvoted answer provided
(points scoring?), the following script IS NON-BLOCKING, and does
not care what length returned input may be.  IE it will work with 
ANY screen size.

With SH it is more complex, and I was unable to find enhanced command line version of the built-in read, eventually I found a mention of dd on STDIN, here is the result. NOTE that the SH version of built-in echo does not permit the use echo -en although /bin/echo -en does work we use printf instead.

#!/bin/sh
x_TERM=`stty -g`
stty -icanon -echo
printf "\033[6n"
ESCPOS=""
X=""
I=0
while [ ! "$X" = "R" ]; do
  X=`dd bs=1 count=1 2>/dev/null`
  I=`expr $I + 1`
  if [ $I -gt 2 -a ! "$X" = "R" ]; then
    ESCPOS="$ESCPOS$X"
  fi
done
stty "$x_TERM"
#echo "$ESCPOS"
CSRLIN=`echo "$ESCPOS" | cut -d \; -s -f 1`
POS=`echo "$ESCPOS" | cut -d \; -s -f 2`
echo "$CSRLIN"
#exit 0 <= dont use inline

I used the same code in two differnt scripts, one outputs CSRLIN, the other POS.

EDIT: you need to inline this script to use it in another script (eg . CSRLIN, as the shell has to be in interactive mode.

Cheers

Paul