【运维经】第31章——expr命令行计数器

运维经–目录

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expr命令行计数器

一般用于在shell下面做计算或部分字符串造作。
表达式说明:
用空格隔开每个项；
用 / (反斜杠) 放在 shell 特定的字符前面；
对包含空格和其他特殊字符的字符串要用引号括起来

1.计算字符串长度

[frank@LAPTOP-0OCJTGJR dev1]$ expr length "hello world"
11

2.取子串

[frank@LAPTOP-0OCJTGJR dev1]$ expr substr "my name is Frank." 4 4
name

3.抓取第一个字符数字串出现的位置

[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr index "my name is Frank." n
4

4.数学计算

[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr index "my name is Frank." n
4
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 1 + 1
2
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 2 - 1
1
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 1+1
1+1 # 需要用空格分开每一项
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 2 * 3
expr: syntax error # `*` 是特殊字符，需要转义`\*`
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 2 \* 3
6
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 6 / 2
3
[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr 11 % 3
2

选项

[frank@LAPTOP-0OCJTGJR 上线开启业务]$ expr --help
Usage: expr EXPRESSION
  or:  expr OPTION

      --help     display this help and exit
      --version  output version information and exit

Print the value of EXPRESSION to standard output.  A blank line below
separates increasing precedence groups.  EXPRESSION may be:

  ARG1 | ARG2       ARG1 if it is neither null nor 0, otherwise ARG2

  ARG1 & ARG2       ARG1 if neither argument is null or 0, otherwise 0

  ARG1 < ARG2       ARG1 is less than ARG2
  ARG1 <= ARG2      ARG1 is less than or equal to ARG2
  ARG1 = ARG2       ARG1 is equal to ARG2
  ARG1 != ARG2      ARG1 is unequal to ARG2
  ARG1 >= ARG2      ARG1 is greater than or equal to ARG2
  ARG1 > ARG2       ARG1 is greater than ARG2

  ARG1 + ARG2       arithmetic sum of ARG1 and ARG2
  ARG1 - ARG2       arithmetic difference of ARG1 and ARG2

  ARG1 * ARG2       arithmetic product of ARG1 and ARG2
  ARG1 / ARG2       arithmetic quotient of ARG1 divided by ARG2
  ARG1 % ARG2       arithmetic remainder of ARG1 divided by ARG2

  STRING : REGEXP   anchored pattern match of REGEXP in STRING

  match STRING REGEXP        same as STRING : REGEXP
  substr STRING POS LENGTH   substring of STRING, POS counted from 1
  index STRING CHARS         index in STRING where any CHARS is found, or 0
  length STRING              length of STRING
  + TOKEN                    interpret TOKEN as a string, even if it is a
                               keyword like 'match' or an operator like '/'

  ( EXPRESSION )             value of EXPRESSION

Beware that many operators need to be escaped or quoted for shells.
Comparisons are arithmetic if both ARGs are numbers, else lexicographical.
Pattern matches return the string matched between \( and \) or null; if
\( and \) are not used, they return the number of characters matched or 0.

Exit status is 0 if EXPRESSION is neither null nor 0, 1 if EXPRESSION is null
or 0, 2 if EXPRESSION is syntactically invalid, and 3 if an error occurred.

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
For complete documentation, run: info coreutils 'expr invocation'