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powershell - PowerShell 字符串插值语法

问题描述

我总是使用以下语法来确保变量在字符串中展开：

"my string with a $($variable)"

我最近遇到了以下语法：

"my string with a ${variable}"

它们是等价的吗？有什么区别吗？

标签： powershellsyntaxstring-interpolation

解决方案

为了补充marsze 的有用答案：

${...}如果变量名包含特殊字符{，例如空格、、或}.-

在字符串扩展（插值） inside的上下文中"..."，还有另一个使用${...}的理由，即使变量名本身不需要它：

如果您需要直接从非空白字符后面描述变量名称，特别是包括:：

$foo = 'bar'  # example variable

# INCORRECT: PowerShell assumes that the variable name is 'foobarian', not 'foo'
PS> "A $foobarian."
A .  # Variable $foobarian doesn't exist -> reference expanded to empty string.

# CORRECT: Use {...} to delineate the variable name:
PS> "A ${foo}barian."
A barbarian.

# INCORRECT: PowerShell assumes that 'foo:' is a *namespace* (drive) reference
#            (such as 'env:' in $env:PATH) and FAILS:
PS> "$foo: bar"
Variable reference is not valid. ':' was not followed by a valid variable name character. 
Consider using ${} to delimit the name.

# CORRECT: Use {...} to delineate the variable name:
PS> "${foo}: bar"
bar: bar

有关 PowerShell 字符串扩展规则的全面概述，请参阅此答案。

请注意，在将不带引号的参数传递给命令的上下文中，隐式应用字符串扩展时，您需要相同的技术；例如：

# INCORRECT: The argument is treated as if it were enclosed in "...",
#            so the same rules apply.
Write-Output $foo:/bar

# CORRECT
Write-Output ${foo}:/bar

最后，一个有点晦涩的替代方法是`-escape 变量名后面的第一个字符，但问题是这仅适用于不属于转义序列的字符（请参阅参考资料about_Special_Characters）：

# OK: because `: is not an escape sequence.
PS> "$foo`: bar"
bar: bar

# NOT OK, because `b is the escape sequence for a backspace character.
PS> "$foo`bar"
baar # The `b "ate" the trailing 'r' of the variable value
     # and only "ar" was the literal part.

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