If an unset variable can't produce a valid result, check for the variable and throw an InvalidArgumentException.
如果未设置的变量无法生成有效的结果,请检查变量并抛出InvalidArgumentException。
If the addsuffix variable is unset, then TCSH displays only documents, which is inconvenient because you need to determine whether documents is a normal file or a folder.
如果取消addsuffix变量,tcsh就只显示documents,这对于判断documents是一般文件还是文件夹很不方便。
To unset a variable, use unset.
使用unset取消变量。
As with the functions built-in variable, type set — erase variable name to "unset," or erase, a variable.
与内置命令functions一样,输入set——erasevariablename就可以删除一个变量。
This is used to set a default value for a variable. If the variable is empty or unset, the given default value is printed instead. Default takes one argument.
此函式用在设定变数的预设值,如果变数的值是空白或尚未设定的话,则会列印出预设值,使用此函式时会预设需要一个参数。
If the variable is empty or unset, the given default value is printed instead. Default takes one argument.
当变量为空或者未分配的时候,将由给定的默认值替代输出。
If the variable is empty or unset, the given default value is printed instead. Default takes one argument.
当变量为空或者未分配的时候,将由给定的默认值替代输出。
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