Linux command
expr 命令
文本
复制后可按需替换文件名、目录或参数。
常用示例
Evaluate arithmetic
expr [5] + [3]
Multiply
expr [5] \* [3]
String length
expr length "[string]"
Substring extraction
expr substr "[string]" [1] [5]
Pattern matching
expr "[string]" : '[regex]'
Compare values
expr [10] \> [5]
Find index
expr index "[string]" "[chars]"
说明
expr evaluates expressions and outputs the result. It handles integer arithmetic, string operations, and comparisons. Results are printed to standard output with exit status indicating boolean results. Operators must be passed as separate arguments, with shell metacharacters escaped. For arithmetic, expr only handles integers. String operations include length, substring extraction, and regex matching. expr is often used in shell scripts for calculations and string manipulation, though modern shells provide built-in alternatives.
参数
- +, -, \*, /, %
- Arithmetic operators (multiply must be escaped).
- =, !=, \<, \>, \<=, \>=
- Comparison operators (escape < and >).
- length _STRING_
- Return string length.
- substr _STRING_ _POS_ _LEN_
- Extract substring (1-indexed).
- index _STRING_ _CHARS_
- Find first occurrence of characters.
- match _STRING_ _REGEX_
- Pattern match (same as STRING : REGEX).
- |
- Logical OR: ARG1 | ARG2 returns ARG1 if non-null and non-zero, else ARG2.
- &
- Logical AND: ARG1 & ARG2 returns ARG1 if both are non-null and non-zero, else 0.
- --help
- Display help information.
- --version
- Display version information.
FAQ
What is the expr command used for?
expr evaluates expressions and outputs the result. It handles integer arithmetic, string operations, and comparisons. Results are printed to standard output with exit status indicating boolean results. Operators must be passed as separate arguments, with shell metacharacters escaped. For arithmetic, expr only handles integers. String operations include length, substring extraction, and regex matching. expr is often used in shell scripts for calculations and string manipulation, though modern shells provide built-in alternatives.
How do I run a basic expr example?
Run `expr [5] + [3]` in a terminal, then adjust file names, paths, flags, or remote targets for your system.
What does +, -, \*, /, % do in expr?
Arithmetic operators (multiply must be escaped).