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shell でネストされた変数を展開したい

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問題

Ruby の bundle install 時に
RAILS_ENV=development なら bundle install --without development
RAILS_ENV=production なら bundle install --without development:test みたいなことをやりたい

例えば

$ config_staging=hoge
$ config_production=fuga
$ target=staging

のとき、 config_${target} の中身の hoge を呼び出したい

解決策

eval を使う

$ echo "$(eval echo \${config_${target}})"
hoge

# or

$ config=\$config_${target}
$ echo $config
$config_staging

$ echo "$(eval echo $config)"
hoge
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