Two conditions in if statment

Question

I'm struggling in if statment

I want the message "The system is highly utilized" pops whenever the memory usage or cpu usage exceeds 70%, now i tried the following 2 conditions in if statment but it gives me error.

# This script monitors CPU and memory usage
RED='\033[0;31m'
NC='\033[0m' # No Color
while :
do
Get the current usage of CPU and memory
limit=70.0
  cpuUsage=$(top -bn1 | awk '/Cpu/ { print $2}')
  memTotal=$(free -m | awk '/Mem/{print $2}')
  memUsage=$(free -m | awk '/Mem/{print $3}')
  memUsage=$(( (memUsage * 100) / memTotal ))
Print the usage
echo "CPU Usage: $cpuUsage%"
  echo "Memory Usage: $memUsage%"
Sleep for 1 second
sleep 1
if  (( $(echo "$cpuUsage > $limit ; $memUsage > $limit" |bc -l) ))
  then
         printf "${RED}The system is highly utilized${NC}\n"
  else
        echo The system is not highly utilized
  fi
done

as far as i know the ; runs checks 1st condition and then goes to the 2nd regardless of success. I get this error anyways: 0 : syntax error in expression (error token is "0 ")

Answer 1

bc understands || and &&.

if (( $(echo "$cpuUsage > $limit || $memUsage > $limit" | bc -l) ))

Answer 2

Although (as you have seen), you can combine expressions using logical || in GNU bc (and in busybox bc), it's not supported by POSIX¹.

Since you're already using awk to parse the top and free outputs, an alternative approach would be to do the arithmetic and relational testing in awk as well - then you can use simple integer comparison in the shell (not even requiring bash):

#!/bin/sh
This script monitors CPU and memory usage
RED='\033[0;31m'
NC='\033[0m' # No Color
limit=${1:-70.0}
while :
do
Get the current usage of CPU and memory
top -bn1 | awk -v limit="$limit" '
    /^%Cpu/ {printf "CPU Usage: %.1f%%\n", $2; exit ($2+0 > limit ? 1 : 0)} 
  '
  cpuHi=$?
free -m | awk -v limit="$limit" '
    /^Mem/ {usage = 100*$3/$2; printf "Memory Usage: %.0f%%\n", usage; exit (usage > limit ? 1 : 0)}
  '
  memHi=$?
sleep 1
if [ "$cpuHi" -ne 0 ] || [ "$memHi" -ne 0 ]
  then
         printf "${RED}The system is highly utilized${NC}\n"
  else
        printf "The system is not highly utilized\n"
  fi
done

---

1. in fact, POSIX bc doesn't even support relational operators outside of a conditional construct or loop, ex.:

    $ echo '2 > 1 || 1 > 2' | bc
    1
   

   but with warnings enabled:

    $ echo '2 > 1 || 1 > 2' | bc -w
    (standard_in) 1: (Warning) || operator
    (standard_in) 2: (Warning) comparison in expression
    1
   

   and similarly with busybox

    $ echo '2 > 1 || 1 > 2' | busybox bc -w
    bc: POSIX does not allow boolean operators; this is bad: ||
    bc: POSIX does not allow comparison operators outside if or loops
    1
   

Answer 3

To expand a bit on @choroba's answer:

echo "$cpuUsage > $limit ; $memUsage > $limit" |bc -l

will output 2 lines.

A demonstration

$ set -x
+ set -x
$ ans=$(echo "1==1; 2==1" | bc -l)
++ bc -l
++ echo '1==1; 2==1'
+ ans='1
0'
$ if (( $ans )); then echo yes; fi
+ ((  1
0  ))
bash: ((: 1
0 : syntax error in expression (error token is "0 ")