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Expand Nested Bash Variables

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[系统(linux) 所属分类 系统(linux) | 发布者 店小二05 | 时间 2017 | 作者 红领巾 ] 0人收藏点击收藏

Consider the following Bash script:

RICK="Rick Sanchez" TINY_RICK='$RICK' echo $TINY_RICK

We nest a variable named “RICK” within another variable named “TINY_RICK”, and as you can probably guess the output of the script will not be the expected “Rick Sanchez”.

This is because Bashwill not recursively resolve variables while evaluating a string, so the output will be:

~ sh ./scripts.sh $RICK Solution We can in fact ask bash to resolve a nested variable using the following syntax [notice the exclamation mark (!) prefixing the variable name] : echo "${!TINY_RICK}" # Resolve the nested variable name

But this is not enough. Remember that our variable contains a literal “$” symbol? Although this is valid syntax, Bash will ignore it as a reference to a variable. So using the exclamation mark (!) will work only if the nested value is the name of the variable sans-prefix.

In order to solve this, we simply strip the first character from the value:

TINY_RICK="${TINY_RICK:1}" # String the first character - a $ echo "${!TINY_RICK}" # Resolve the nested variable name

and now our script:

RICK="Rick Sanchez" TINY_RICK='$RICK' TINY_RICK="${TINY_RICK:1}" echo ${!TINY_RICK}

Will output “Rick Sanchez”!

本文系统(linux)相关术语:linux系统 鸟哥的linux私房菜 linux命令大全 linux操作系统

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