You can check if a directory exists in a shell script by using the if statement in combination with the test command or the [ command.
For example, using the test command:
if [ -d "/path/to/directory" ]; then
  echo "Directory exists"
else
  echo "Directory does not exist"
fi
Using the [ command:
if [ -d "/path/to/directory" ]
then
  echo "Directory exists"
else
  echo "Directory does not exist"
fi
In both examples, the -d option is used to test for the existence of a directory. The if statement evaluates the result of the test or [ command and prints a message depending on whether the directory exists or not.