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Introduction
In bash, the usage of the colon and the lying colon is different, so be careful not to use it wrong.
a lying colon is two dots
难道正常的不是两个点）的作用：
A sequence expression takes the form {x…y[…incr]}, where x and y are either integers or single characters, and incr, an optional increment, is an integer. When integers are supplied, the expression expands to each number between x and y, inclusive. Supplied integers may be prefixed with 0 to force each term to have the same width. When either x or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary. When characters are supplied, the expression expands to each character lexicographically between x and y, inclusive, using the default C locale. Note that both x and y must