spawn.sh

Shall高级编程

#!/bin/bash
# spawn.sh


PIDS=$(pidof sh $0)  # Process IDs of the various instances of this script.
P_array=( $PIDS )    # Put them in an array (why?).
echo $PIDS           # Show process IDs of parent and child processes.
let "instances = ${#P_array[*]} - 1"  # Count elements, less 1.
                                      # Why subtract 1?
echo "$instances instance(s) of this script running."
echo "[Hit Ctl-C to exit.]"; echo


sleep 1              # Wait.
sh $0                # Play it again, Sam.

exit 0               # Not necessary; script will never get to here.
                     # Why not?

#  After exiting with a Ctl-C,
#+ do all the spawned instances of the script die?
#  If so, why?

# Note:
# ----
# Be careful not to run this script too long.
# It will eventually eat up too many system resources.

#  Is having a script spawn multiple instances of itself
#+ an advisable scripting technique.
#  Why or why not?