trap.sh | trap (CTRL-C) is signal 2 (SIGINT)

 cat trap.sh
#!/bin/usr/env bash

trap 'increment' 2

increment()
{
  echo "Caught SIGINT ..."
  X=`expr ${X} + 500`
  if [ "${X}" -gt "2000" ]
  then
    echo "Okay, I'll quit ..."
    exit 1
  fi
}

### main script
X=0
while :
do
  echo "X=$X"
  X=`expr ${X} + 1`
  sleep 1
done

Here is a table of some of the common interrupts:

Number	SIG	Meaning
0	0	On exit from shell
1	SIGHUP	Clean tidyup
2	SIGINT	Interrupt
3	SIGQUIT	Quit
6	SIGABRT	Abort
9	SIGKILL	Die Now (cannot be trap'ped)
14	SIGALRM	Alarm Clock
15	SIGTERM	Terminate