Use /proc/meminfo file to check available memory for system and warn based on given argument thresholds

check_memory.sh

#!/bin/bash

# Set thresholds from script args
WARN_THRESHOLD=$1
CRIT_THRESHOLD=$2

# Find current memory status from /proc/meminfo
current=$(head -n 3 /proc/meminfo)
memtotal=$(expr $(echo $current | awk '{ print $2 }') / 1024)
memfree=$(expr $(echo $current | awk '{ print $5 }') / 1024)
memused=$(expr ${memtotal} - ${memfree})

# Use bc to do floating-point calculation in bash
MemPercentDecimal=$(echo "scale=2; ${memused} / ${memtotal} * 100" | bc)

# Use string formatting to convert back to integer for comparison operators
MemPercent=$(echo ${MemPercentDecimal%%.*})

# Check exit status of boolean comparison commands to set flags
[[ $MemPercent -ge $WARN_THRESHOLD && $MemPercent -lt $CRIT_THRESHOLD ]]; warning=$?
[[ $MemPercent -ge $CRIT_THRESHOLD ]]; critical=$?

if [ $warning -eq 0 ]; then
    echo "WARNING: ${MemPercent}% ${memused}/${memtotal}MB RAM Used"
    exit 2;
elif [ $critical -eq 0 ]; then
    echo "CRITICAL: ${MemPercent}% ${memused}/${memtotal}MB RAM Used"
    exit 1;
else
    echo "OK: ${MemPercent}% ${memused}/${memtotal}MB RAM Used"
    exit 0;
fi