Bash capture a keystroke from another terminal - bash

Question

Using bash 4.3 and root powers, I want to be able to detect one keystroke (any key) from another terminal.
In terminal 1, a background process that writes to a named pipe once one character was read from another tty, say pts/18
read -rsn1 < /dev/pts/18 && echo > ./myfifo &
In terminal 2, an attempt to read a character from the same fifo
read -rsn1 < ./myfifo
It works moderately well, but only after several (3 or 4) keystrokes in pts/18, not the first one.
The mechanism appears to be redundant but it allows to start several background processes with different ttys and redirect to the same named pipe.
Hope you can help me.

Answer 1

One day I've tried to do that.
Wrote script who getting that you want with strace:
#!/bin/bash
# Couple of special symbols
BACKSPACE='\10\33[K'
BACKSPACE_EMPTY='\7'
BACKSLASH='\\'
QUOTE="\'"
DOUBLE_QUOUTE='\"'
LARROW='\10'
RARROW='\33[C'
#APPOSTRO="'\`'"
BACKSPACE_='\\33\[1P'
#LOGDATE=`date '+%Y/%m/%d %H:%M:%S'`
BADBIN='\\33\]'
while read -r line
do
# Avoiding binary symbols
NOBINline=$(echo "${line}" | strings)
# Current `pwd` value for session
CURRENT_PWD_OF_PID=$(readlink -f /proc/${1}/cwd)
# Getting username
USER_OF_PID=$(cat /proc/${1}/environ | strings | tr '.' ' ' | grep USER | awk -F= '{print $2}')
# Not the best but working way to create prompt line
HOSTNAME_OF_PID=`hostname -a`
STR_TO_REMOVE=$(printf "${USER_OF_PID}""#""${HOSTNAME_OF_PID}"":""${CURRENT_PWD_OF_PID}")
# Cut useless symbols from strace output.
parsed_line=$(echo "${NOBINline}" | perl -nale 'print $1 if ~/\"(.*)\"/gi')
if [ "${parsed_line}" == "\n" ]
then
parsed_line="{{ENTER}}"
fi
output_line=''
inchar_line=''
postinchar_line=''
inchar_line=$(printf "${parsed_line}")
if [ "${inchar_line}" == "{{ENTER}}" ]
then
echo ""
else
output_line=$(printf "${output_line}""${inchar_line}")
fi
if [ "${output_line}" != "${CURRENT_PWD_OF_PID}" -a "${output_line}" != "${STR_TO_REMOVE}" -a `echo "${NOBINline}" | grep -c "${BADBIN}"` -eq 0 ]
then
printf "${output_line}"
fi
done < <(sudo strace -e trace=write -s1000 -p $1 2>/dev/stdout)
How to use:
./script.sh <PID_of_mointored_console>
Also I've written the second script (much more ugly than first):
#!/bin/bash
while [ 1 ]
do
# lets and log_start -- names of two my scripts.
for PIDs in `ps awwux | grep [p]ts | grep bash | grep -v lets | grep -v log_start | grep -v grep | awk '{print $2}'`
do
PTS=$(ps awwux | grep "${PIDs}" | grep -v grep | awk '{print $7}')
if [ -f /tmp/bash_log.${PIDs} ]
then
sleep 1
else
touch /tmp/bash_log.${PIDs}
# lets.sh -- first script.
/bin/bash /root/lets.sh $PIDs >> /tmp/bash_log.${PIDs} &
fi
# tr -cd '\11\12\15\40-\176' < /tmp/x_bash_log.${PIDs} | sed 's/\]0;//g' | sed 's/\[C//g' > /tmp/bash_log.${PIDs}
done
for IFEMPTY in `find /tmp/ -type f -name 'bash_log*' -mmin +600`
do
if [ `cat "${IFEMPTY}" | grep -v "\'" | wc -c` -lt 2 ]
then
rm -rf "${IFEMPTY}"
else
sleep 1
fi
done
done
Start it in the background, place near first script.
It will catching all new terminal sessions, and start firstscript.sh <PID> for each, and creating /tmp/bash_log.<PID> file.
How to use:
./monitor.sh &
# Start new terminal
[sahaquiel#sahaquiel-PC ~]$ echo $$
916
[sahaquiel#sahaquiel-PC ~]$ HELO, IM A NEW STRING
bash: HELO,: command not found
[sahaquiel#sahaquiel-PC ~]$ tail -n3 /tmp/bash_log.916
916
''[sahaquiel#sahaquiel-PC ~]$ HELO, IM A NEW STRING
'''[sahaquiel#sahaquiel-PC ~]$ tail -n3 /tmp/bash_log.916
NB. I'm still working with it, created just for fun.
/tmp/bash_log files have awful formatting. I've also tried to log in the file backslashes, Ctrl+R, Ctrl+C and the same, but at now it's looks like not readable enough:
'''[sahaquiel#sahaquiel-PC ~]$ I WILL TYPE BACKSLASH THREE TIMES IN THE END OF THIS STRING 123[BACKSPACE] [Backspace found. Rewritten string]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ I WILL TYPE BACKSLASH THREE TIMES IN THE END OF THIS STRING 12[BACKSPACE] [Backspace found. Rewritten string]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ I WILL TYPE BACKSLASH THREE TIMES IN THE END OF THIS STRING 1[BACKSPACE] [Backspace found. Rewritten string]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ I WILL TYPE BACKSLASH THREE TIMES IN THE END OF THIS STRING
'''[sahaquiel#sahaquiel-PC ~]$ NOW I I[BACKSPACE] [Backspace found. Rewritten string]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ NOW I WILL PRESS \"LEFT ARROW\" THREE TIMES[LARROW] [Left arrow found.]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ NOW I WILL PRESS \"LEFT ARROW\" THREE TIME[LARROW]S[LARROW] [Left arrow found.]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ NOW I WILL PRESS \"LEFT ARROW\" THREE TIM[LARROW]ES[LARROW] [Left arrow found.]: └────>
'''[sahaquiel#sahaquiel-PC ~]$ NOW I WILL PRESS \"LEFT ARROW\" THREE TI[LARROW]MES
You can change it somehow you want.
There are a lot of variables, I wanted to use them later for extended strings parse way, but it doesn't work now correctly.
P.S. If someone really interested in that, can check this project on my Github (check profile for link)