Bash：附加到带有变量名称的列表
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Bash: Append to list with variable name
提问by user1837378
The first three commands work but the fourth does not. How can I append to an array with a variable in its name?
前三个命令有效，但第四个命令无效。如何附加到名称中带有变量的数组？
i=4
eval pim$i=
pim4+=(`date`)
pim$i+=(`date`)
Thanks!
谢谢！
回答by Charles Duffy
With bash 4.3, there's a feature targeted at just this use case: namerefs, accessed with declare -n. (If you have a modern ksh, they're also available using the namerefbuilt-in)
在 bash 4.3 中，有一个专门针对此用例的功能：namerefs，使用declare -n. （如果你有一个现代的ksh，它们也可以使用nameref内置的）
declare -n pim_cur="pim$i"
pim_cur+=( "$(date)" )
With bash 4.2, you can use printf -vto assign to array elements:
使用 bash 4.2，您可以使用printf -v分配给数组元素：
array_len=${#pim4[@]}
printf -v "pim4[$array_len]" %s "$(date)"
Prior to bash 4.2, you may need to use eval; this can be made safe by using printf %qto preprocess your data:
在 bash 4.2 之前，您可能需要使用 eval；这可以通过使用printf %q预处理您的数据来确保安全：
printf -v safe_date '%q' "$(date)"
eval "pim$i+=( $safe_date )" # only safe if you can guarantee $i to only contain
# characters valid inside a variable name (such as
# numbers)
