Bash scripts

## Check params number is 1

if [ "$#" -ne 1 ]; then
    echo "Number of parameters is not one"
    exit
fi

## Check a variable is empty

[ -z "$var" ] && echo "Empty" || echo "Not empty"

## Check a cmd exists or not
command -v wget >/dev/null 2>&1 || { echo >&2 "wget is not installed. Aborting."; exit 1; }