How to know command is installed in shell

Question

In xxx.sh, I need to execute a command. But if this command is not found, I want to throw an error.

if [[ xxxxxxx ]]; then
    echo "sorry xx command not found"
    exit 1
fi

Answer 1

From this answer:

In summary:

Where bash is your shell/hashbang, consistently use hash (for commands) or type (to consider built-ins & keywords).

When writing a POSIX script, use command -v.