January 2024
Intermediate to advanced
472 pages
5h 56m
Japanese
Content preview from Rustの練習帳 ―コマンドラインツールの作成を通してRustを学ぶBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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4章headコマンド
変化のために何でもしよう / 自分のものとするために握手をしよう
—— They Might Be Giants, "Stand on Your Own Head" (1988)
本章では、headコマンドのクローンを作成します。headは、1つ以上のファイルの最初の数行または数バイトを表示するコマンドです。テキストファイルの中身を少しだけ見たいときによく使われます。また、あるプロセスが出力した複数のファイルがある場合に使うと、問題をすばやく把握できます。とくに、非常に大きなファイルを扱うときには、ファイル全体を読み込むcatより、headのほうが便利です。
本章では、次の内容を学びます。
- 値を受け取るオプション引数の作成
- 文字列を数値に変換する方法
- 単体テストの作成と実行
matchアームとガードの併用From、Into、asを用いた型の変換- イテレータやファイルハンドルで
takeを使う方法 - 改行を保持したままファイルハンドルを読み込む方法
- ファイルハンドルからバイトと文字を読み込む方法
- ターボフィッシュ演算子の使い方
4.1 headの動作
まずはheadの概要から説明します。Berkeley Standard Distribution（BSD）、SunOS/Solaris、HP-UX、Linuxなど、オリジナルのAT&T Unix OSの実装は数多く存在します。ほとんどのOSにはheadコマンドがあり、デフォルトでは1つ以上のファイルの最初の10行を表示します。また、多くの場合、表示する行数を制御するためのオプション-nと、表示するバイト数を制御するためのオプション-cがあります。man headを実行すると、BSD版にはこの2つのオプションだけがあることがわかります。 ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.