#Bash 的 expr 命令

expr EXPRESSION

功能

计算表达式。

类型

可执行文件（/usr/bin/expr），属于 coreutils。

参数

• EXPRESSION 表达式：
  • ARG1 | ARG2 - 如果 ARG1 不是 0 或 null，则结果为 ARG1，否则为 ARG2
  • ARG1 & ARG2 - 如果 ARG1 和 ARG2 都不是 0 或 null，则结果为 ARG1，否则为 0
  • ARG1 < ARG2 - ARG1 ARG2
  • ARG1 <= ARG2 - ARG1 ARG2
  • ARG1 = ARG2 - ARG1 ARG2
  • ARG1 != ARG2 - ARG1 ARG2
  • ARG1 >= ARG2 - ARG1 ARG2
  • ARG1 > ARG2 - ARG1 ARG2
  • ARG1 + ARG2 - ARG1 ARG2；仅支持整数，下同
  • ARG1 - ARG2 - ARG1 ARG2
  • ARG1 * ARG2 - ARG1 ARG2
  • ARG1 / ARG2 - ARG1 ARG2
  • ARG1 % ARG2 - ARG1 ARG2
  • STRING : REGEXP - 在字符串 STRING 中使用正则表达式 REGEXP 进行锚定匹配
  • match STRING REGEXP - 同 STRING : REGEXP
  • substr STRING POS LENGTH - 从字符串 STRING 中 POS 位置（从 1 开始）截取长度为 LENGTH 的子串
  • index STRING CHARS - 从字符串 STRING 中查找 CHARS 中任意字符首次出现的位置，找不到则得到 0
  • length STRING - 获取字符串 STRING 的长度
  • ( EXPRESSION ) - 括号嵌套表达式
• OPTION 选项：
  • --help - 显示帮助
  • --version - 显示版本

#示例

$ expr 1 '>' 3                     # 判断大于
0
$ expr 1 + 1                       # 加法
2
$ expr 2 - 3                       # 减法
-1
$ expr 10 / 3                      # 除法
3
$ expr 10 % 3                      # 取余
1
$ expr length primers              # 获取 primers 的长度
7
$ expr index primers aeiou         # 在 primers 中查找 aeiou 中的任意一个字符位置
3
$ expr substr primers 3 3          # 从 primers 中 3 位置截取长度为 3 的子串
ime
$ expr match 'https://xplanc.org/primers/' 'https\?://[^/]*/\(.*\)'
primers/

#推荐阅读

• Evaluate expressions - GNU Coreutils
• expr(1) — Linux manual page

#手册

显示
EXPR(1)                          User Commands                         EXPR(1)

NAME
       expr - evaluate expressions

SYNOPSIS
       expr EXPRESSION
       expr OPTION

DESCRIPTION
       --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 lexicographi‐
       cal.   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 er‐
       ror occurred.

AUTHOR
       Written by Mike Parker, James Youngman, and Paul Eggert.

REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT
       Copyright © 2023 Free Software Foundation, Inc.   License  GPLv3+:  GNU
       GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
       This  is  free  software:  you  are free to change and redistribute it.
       There is NO WARRANTY, to the extent permitted by law.

SEE ALSO
       Full documentation <https://www.gnu.org/software/coreutils/expr>
       or available locally via: info '(coreutils) expr invocation'

GNU coreutils 9.4                 April 2024                           EXPR(1)