Linux - [

于 2009-02-22 14:57:00 发布 · 73 阅读

Linux - [

[: [ arg... ]
This is a synonym for the "test" builtin, but the last argument must be a literal `]', to match the opening `['.
[[ ... ]]: [[ expression ]]
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. The && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to determine the expression's value.