$BASHPID

The following example shows how regular PID (Process ID) $$ fails to get the correct PID for a subshell. While $BASHPID gives the correct PID

 
unhappy_func(){
  echo "unhappy_func triggered (BASHPID: $BASHPID, PID=$$)"
 
  return 1
}
 
happy_func(){
  echo "happy_func triggered (BASHPID: $BASHPID, PID=$$)"
 
  return 0
}
 
main() {
  echo "main PID: $$"
 
  happy_func && (unhappy_func || return 1)
 
  echo.green "happy finish"
}
 
main "${@}" || echo.red "Unhappy finish"

The output looks like

main PID: 9200
happy_func triggered (BASHPID: 9200, PID=9200)
unhappy_func triggered (BASHPID: 9201, PID=9200)
happy finish

Also note $BASHPID does not work in zsh.

Related

• parenthesis-spawn-a-subshell