如何在bash中连接数组？

Question

我是一个新__CODE__学习者.我有一个数组__CODE__从标准输入中获取输入.我必须连接两次.说,我在数组中有以下元素:

Namibia
Nauru
Nepal
Netherlands
NewZealand
Nicaragua
Niger
Nigeria
NorthKorea
Norway

现在,输出应该是:

Namibia Nauru Nepal Netherlands NewZealand Nicaragua Niger Nigeria NorthKorea Norway Namibia Nauru Nepal Netherlands NewZealand Nicaragua Niger Nigeria NorthKorea Norway

我的代码是:

countries=()
while read -r country; do
    countries+=( "$country" )
done
countries=countries+countries+countries # this is the wrong way, i want to know the right way to do it
echo "${countries[@]}"

请注意,我可以像下面的代码一样打印三次,但这不是我的座右铭.我必须在数组中连接它们.

countries=()
while read -r country; do
    countries+=( "$country" )
done
echo "${countries[@]} ${countries[@]} ${countries[@]}"

Answer 1

首先,要将列表读入数组,每行一个条目:

readarray -t countries

...或者,对于旧版本的bash:

# same, but compatible with bash 3.x; || is to avoid non-zero exit status.
IFS=$'\n' read -r -d '' countries || (( ${#countries[@]} ))

其次,要复制条目,要么将数组展开为自身三次:

countries=( "${countries[@]}" "${countries[@]}" "${countries[@]}" )

...或使用现代语法执行追加:

countries+=( "${countries[@]}" "${countries[@]}" )

Answer 2

简单地写这个：

countries=$(cat)
countries+=( "${countries[@]}" "${countries[@]}" )
echo ${countries[@]}

第一行是输入数组，第二行是连接数组，最后一行是打印数组。