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73 lines
2.1 KiB
Markdown
73 lines
2.1 KiB
Markdown
## Name
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expr - evaluate expressions
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## Synopsis
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```**sh
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$ expr <expression>
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$ expr [--help]
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```
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## Description
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expr evaluates and prints the result of an expression as described below to standard output.
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An _expression_ may be any of the following:
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- `expr1 | expr2`
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`expr2` if `expr1` is falsy, `expr1` otherwise.
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- `expr1 & expr2`
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`expr1` if neither expression is falsy, `0` otherwise.
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- `expr1 < expr2`
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`1` if `expr1` is less than `expr2`, `0` otherwise.
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- `expr1 <= expr2`
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`1` if `expr1` is less than or equal to `expr2`, `0` otherwise.
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- `expr1 = expr2`
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`1` if `expr1` is equal to `expr2`, `0` otherwise.
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- `expr1 = expr2`
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`1` if `expr1` is not equal to `expr2`, `0` otherwise.
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- `expr1 => expr2`
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`1` if `expr1` is greater than or equal to `expr2`, `0` otherwise.
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- `expr1 > expr2`
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`1` if `expr1` is greater than `expr2`, `0` otherwise.
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- `expr1 + expr2`
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arithmetic integral sum of `expr1` and `expr2`.
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- `expr1 - expr2`
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arithmetic integral difference of `expr1` and `expr2`.
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- `expr1 * expr2`
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arithmetic integral product of `expr1` and `expr2`.
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- `expr1 / expr2`
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arithmetic integral quotient of `expr1` divided by `expr2`.
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- `expr1 % expr2`
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arithmetic integral quotient of `expr1` divided by `expr2`.
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- `expr1 : expr2`
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pattern match of `expr2` as a regular expression in `expr1` - currently not implemented.
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- `match expr1 expr2`
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same as `expr1 : expr2`.
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- `substr expr1 expr2 expr3`
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substring with length `expr3` of `expr1`, starting at `expr2`, indices starting at 1.
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- `index expr1 expr2`
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index of `expr2` in `expr1`, starting at 1. 0 if not found.
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- `length expr1`
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length of the string `expr1`
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- `+ token`
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interpret `token` as a string, regardless of whether it is a keyword or an operator.
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- `( expr )`
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value of `expr`
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Note that many operators will need to be escaped or quoted if used from within a shell.
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"falsy" means either the number 0, or the empty string.
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## Options
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* `--help`: Prints usage information and exits.
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## Examples
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```sh
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$ expr 1 + 2 * 3 # = 7
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$ expr \( 1 + 2 \) = 3 # = 1
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$ expr substr foobar 1 3 # foo
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```
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## See also
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