?
if ! [ -f /path/to/file ]; then
echo 'No file'
fi

if ! [ -d /path/directory/ ]; then
echo 'No directory'
fi

grep "username:" /etc/passwd >/dev/null
if [ $? -ne 0 ]; then
echo 'No username found'
fi

#!/bin/bash
# автор: https://t.iss.one/bash_srv
# This script monitors CPU and memory usage

while :
do 
  # Get the current usage of CPU and memory
  cpuUsage=$(top -bn1 | awk '/Cpu/ { print $2}')
  memUsage=$(free -m | awk '/Mem/{print $3}')

  # Print the usage
  echo "CPU Usage: $cpuUsage%"
  echo "Memory Usage: $memUsage MB"
 
  # Sleep for 1 second
  sleep 1
done