expr EXPRESSION
!subtitle:功能
计算表达式。
!subtitle:类型
可执行文件（/usr/bin/expr），属于 coreutils。
!subtitle: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 $ \lt $ ARG2
ARG1 <= ARG2 - ARG1 $ \le $ ARG2
ARG1 = ARG2 - ARG1 $ = $ ARG2
ARG1 != ARG2 - ARG1 $ \ne $ ARG2
ARG1 >= ARG2 - ARG1 $ \ge $ ARG2
ARG1 > ARG2 - ARG1 $ \gt $ ARG2
ARG1 + ARG2 - ARG1 $ + $ ARG2；仅支持整数，下同
ARG1 - ARG2 - ARG1 $ - $ ARG2
ARG1 * ARG2 - ARG1 $ \times $ ARG2
ARG1 / ARG2 - ARG1 $ \div $ ARG2
ARG1 % ARG2 - ARG1 $ \text{mod} $ 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
$ 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/
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)