minigrep Rust圣经入门练习项目 Usage 大小写敏感查找 cargo run -- to poem.txt 忽略大小写敏感查找 IGNORE_CASE=1 cargo run -- to poem.txt 命令行忽略大小写敏感查找 cargo run -- to poem.txt ignore_case cargo run -- to poem.txt IGNORE_CASE