command_substitution

UP="uptime"
echo $UP
  print - uptime

(here ` = backtick)
UP=`uptime`     
echo $uptime
  print = 19:27:41 up  1:05,  6 users,  load average: 0.00, 0.00, 0.00

CURRENT_USER=$(who)
echo $CURRENT_USER
  print = ubuntu pts/0 2023-10-21 18:23 (49.36.139.64) ubuntu pts/1 2023-10-21 18:23 (49.36.139.64) ubuntu pts/2 2023-10-21 18:54 (49.36.139.64) ubuntu pts/3 2023-10-21 18:54 (49.36.139.64) ubuntu pts/4 2023-10-21 19:12 (49.36.139.64) ubuntu pts/5 2023-10-21 19:12 (49.36.139.64)


free -m 
               total        used        free      shared  buff/cache   available
Mem:             949         192         354           1         402         600
Swap:              0           0           0


free -m | grep Mem
  Mem:             949         192         354           1         402         600

FREE_RAM=`free -m | grep Mem | awk '{print $4}'`
echo "Free RAM is $FREE_RAM mb."     
  print - Free RAM is 354 mb.

  

--------------------------------------------------------------------------------------------------------------------------------------------------------------
#!/bin/bash

echo "Welcome $USER on $HOSTNAME."
echo "******************************************************"

FREE_RAM=$(free -m | grep Mem | awk '{print $4}')
LOAD=$(uptime | awk '{print $9}')
ROOTFREE=$(df -h | grep 'dev/root' | awk '{print $4}')

echo "******************************************************"
echo "Available free RAM is $FREE_RAM MB"
echo "******************************************************"

echo "******************************************************"
echo "Current Load Average $LOAD"
echo "******************************************************"

echo "******************************************************"
echo "Free ROOT partition size is $ROOTFREE"
echo "******************************************************"

echo ""
echo ""
echo ""