pmd.sh

#!/bin/bash

ifthere() {
    for cmd in "$@"
    do
        type ${cmd%% *} >/dev/null 2>&1 && { $cmd || continue; return $?; }
    done
}

usage() {
    cat >&2 <<-EOF
	Usage: $0 [OPTION]...
	Print CPU, memory or disk utilization using available tools.

	Options:
	-m             Memory
	-p or -c       Processor (CPU)
	-d             Disk
	EOF
}

while getopts "mpcdh" opt; do
  case $opt in
    m)
      ifthere \
          free \
          vm_stat
      ;;
    p|c)
      ifthere \
          sar \
          mpstat \
          "ps -e -o pcpu -o pid -o user -o args"
      ;;
    d)
      ifthere \
          df
      ;;
    *)
	  usage
      ;;
  esac
done

test $# -lt 1 && usage