使用[和[[

Question

之间的确切区别是什么？

if [ $? -ne 0 ];

和

if [[ $? -ne 0 ]];

Answer 1

如前所述这里 ：

与[ ， [[相反，可防止变量值的单词分割。 因此，如果VAR="var with spaces" ，则无需在测试中双引号$VAR VAR-尽管使用引号仍然是一个好习惯。 另外， [[防止路径名扩展，因此带有通配符的文字字符串不会尝试扩展为文件名。 使用[[ ， ==和!=将右边的字符串解释为要与左边的值匹配的shell球形模式，例如： [[ "value" == val* ]] 。

Answer 2

空无一人。 不过， [[ ... ]]语法介绍了您可以使用条件表达式执行的其他操作。 来自help [[ ：

Returns a status of 0 or 1 depending on the evaluation of the conditional
expression EXPRESSION.  Expressions are composed of the same primaries used
by the `test' builtin, and may be combined using the following operators:

  ( EXPRESSION )    Returns the value of EXPRESSION
  ! EXPRESSION              True if EXPRESSION is false; else false
  EXPR1 && EXPR2    True if both EXPR1 and EXPR2 are true; else false
  EXPR1 || EXPR2    True if either EXPR1 or EXPR2 is true; else false

When the `==' and `!=' operators are used, the string to the right of
the operator is used as a pattern and pattern matching is performed.
When the `=~' operator is used, the string to the right of the operator
is matched as a regular expression.