$ {VERSION:2:1} =〜[UZ]的含义

Question

以下表达式的含义是什么？

${VERSION:2:1} =~ [U-Z]

Answer 1

它检查变量的第3个字符$VERSION是否是U和之间的字符Z.

• ${var:M:N}N从M位置开始打印字符:

  $ v="12345"
  $ echo ${v:2:1}
  3
  

• =~ 是一个正则表达式比较.

• [U-Z]是从一个范围U到Z.

测试

$ v="abWcd"
$ [[ ${v:2:1} =~ [U-Z] ]] && echo "yes" || echo "no"
yes

$ v="abAcd"
$ [[ ${v:2:1} =~ [U-Z] ]] && echo "yes" || echo "no"
no