Shell bracket operator

The following is an explanation under the bash environment.

One, single parenthesis ()

Two, double parenthesis (())

Can be used as a numerical condition or as a numerical operation (approximate to let command)

Like the C language syntax, supports operators:<<, <<=, >>, >>=, + + 、--、 &, &=, |, |=, ~ 、!、 ^, ^=, + 、-、 *,/,%

Three, single brackets []

[] is actually shorthand for the test command in bash, where [expr] is equivalent to test expr

Numerical tests:-eq,-ne,-gt,-lt,-ge,-le

String Test: =,! =,-Z,-n

File tests:-D,-B,-S,-F,-W,-L,-u,-r,-X

Iv. double brackets [[]]

Follow the traditional C programming syntax.

For strings compared to numbers, if the string cannot be converted to a number, the string is assigned a value of 0.

Five, Canda brackets {}

Not to be continued ...

Shell bracket operator