linux - Bash 脚本如果为 null，则为 true 时评估为 false

Question

我在 shell 脚本编写之旅中遇到了第二个障碍。我似乎无法让我的 if 语句对于空值评估为 true。我试图将参数传递给脚本，并让脚本告诉我是否缺少所需的变量。不幸的是，即使它应该将该变量评估为空值，它仍然会陷入 else 语句。这是脚本:

if [ "$1" == "d" ]; then

        if [ -n "$2" ]; then
            echo "Please enter the local location of the files"
        else
            LOCAL=$2
            scp -r -i ~/Dropbox/Business/aws/first.pem $LOCAL ubuntu@54.XXX.194.202:~/test/
        fi

    else
        scp -r -i ~/Dropbox/Business/aws/first.pem ~/Dropbox/Business/aws/files/binaryhustle/ ubuntu@54.XXX.194.202:~/test/
    fi

这是我运行的用于执行脚本的命令:` bash copyfile.sh d

我得到的回复是:

用法:scp [-12346BCpqrv] [-c 密码] [-F ssh_config] [-i 身份文件]
[-l 限制] [-o ssh_选项] [-P 端口] [-S 程序]
[[user@]host1:]file1 ... [[user@]host2:]file2`

Answer 1

总结一下评论，添加一个函数来消除代码重复:

#!/bin/bash

keyfile=~/Dropbox/Business/aws/first.pem 
destination=ubuntu@54.XXX.194.202:~/test/
default_source=~/Dropbox/Business/aws/files/binaryhustle/

do_copy() {
    source=$1
    scp -r -i $keyfile "$source" "$destination"
}

if [ "$1" == "d" ]; then
    if [ -z "$2" ]; then
        echo "Please enter the local location of the files"
    else
        do_copy "$2"
    fi
else
    do_copy "$default_source"
fi