Bash-common-checks

Common checks and validations that are a PITA to remember

Is Integer?

• Check if a var is an integer
• support negative as well as positive integer values using extended regex

VAR=123
if [[ ${VAR} =~ ^-?[0-9]+$ ]]; then
  echo "Is integer"
else
  echo "Is not integer"
fi

TCP port check

• leverage /dev
• use timeout for sanity
• Use for any kind of TCP knock
• do not use FQDN, go by IP

IP=192.168.15.100
timeout 1 bash -c "</dev/tcp/${IP}/22"
if [[ $? -ne 0 ]]; then
  echo "ssh port closed at $IP"
else
  echo "ssh port open at $IP"
fi