make shell script wait and send signal to recover it

[esolve]

when running a shell script
I want to make it wait for a signal somewhere inside the script,
like

function pause(){
   read -p "$*"
}
echo "start"
pause
echo "stop"

and then send a signal(when some conditions are satisfied) to make the script continue

is it possible or not?
thanks!

[atreyu]

sure, use bash's trap function and a for or while loop.

e.g.:

#!/bin/bash

function some_command() {
  echo "sent $0 a SIGUSR1 signal, so doing command..."
}

trap "some_command" SIGUSR1

while :; do
  echo sleeping
  sleep 1
done

untested code, but that is the general idea.

[esolve]

I'm not familiar with this, can you make it more clear?
thanks

sure, use bash's trap function and a for or while loop.

e.g.:

#!/bin/bash

function some_command() {
  echo "sent $0 a SIGUSR1 signal, so doing command..."
}

trap "some_command" SIGUSR1

while :; do
  echo sleeping
  sleep 1
done

untested code, but that is the general idea.

[atreyu]

I'm not familiar with this, can you make it more clear?

The trap bash function will detect when a signal is sent to the script in which it has been set. You can send a signal to any program (or script) using "kill -$SIGNAL" where $SIGNAL is one of the signals listed by "kill -l" (lower case L).

There is an updated version of the script at the bottom of the post. Copy it to a file called "script.sh". In one terminal, run this script. e.g.:

./script.sh

it will show output like this:

program script.sh, pid 16501 is sleeping...
program script.sh, pid 16501 is sleeping...

then in another terminal, send the pid of the script (16501 in this case) the signal you define in script (i use SIGUSR1 but you can use others) using the kill command, e.g.:

kill -SIGUSR1 16501

and you'll see this in the output of the script.sh in the first terminal:

program trap.sh, pid 16501 is sleeping...
sent ./trap.sh a SIGUSR1 signal, so doing command...
do something, like kill some app, or quit this app
i think i will exit

obviously you'll want to modify script.sh to run what you want.

here's the code:

#!/bin/bash
prog=${0##*/}
function some_command() {
  echo "sent $0 a SIGUSR1 signal, so doing command..."
  pause=1
}

trap "some_command" SIGUSR1

while :; do

  if test $pause; then
    echo do something, like kill some app, or quit this app
    echo i think i will exit
    exit
  fi

  echo program $prog, pid $$ is sleeping...
  sleep 1
done