预期的 Bash 一元运算符
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原文地址: http://stackoverflow.com/questions/15522018/
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Bash Unary Operator Expected
提问by ThePGtipsy
Okay, so within my script (this is my first time working with bash) I am being met with 2 unary operator expected errors. The code itself is actually working fine, but it's presenting me with these errors at runtime.
好的，所以在我的脚本中（这是我第一次使用 bash），我遇到了 2 个一元运算符预期错误。代码本身实际上工作正常，但它在运行时向我展示了这些错误。
[: !=: unary operator expected
for the line
对于线
if [ ${netmask[1]} != "" ]; do
so for the first error, it's thrown when ${netmask[1]}is ""(null), I have tried multiple ideas and still can't get it to work without returning that error in the process
所以对于第一个错误，当它抛出${netmask[1]}是""（null），我已经尝试了多种想法，但仍不能得到工作，而在这个过程中返回的错误
Any help would be appreciated!
任何帮助，将不胜感激！
EDIT:Solved by adding quotation marks (grrr)
编辑：通过添加引号解决（grrr）
if [ "${netmask[1]}" != "" ]; do
采纳答案by kamituel
If you want to check for the nullvalue for a variable, use -zoperator:
如果要检查null变量的值，请使用-z运算符：
if [ -z "${netmask[1]}" ]; then
On example:
例如：
VAR=""
if [ -z "$VAR" ]; then
echo This will get printed
fi
Edit:Please note the parentheses around the variable: "$VAR".
编辑：请注意变量周围的括号："$VAR"。
