wait_on を Homebrew, MacPorts でインストール

プロジェクトリンク

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• wait_on

プロジェクトの歴史

The FreeBSD manual page gives the clearest project history: `wait_on` was written by Andrew Stevenson in January 2002 under FreeBSD 4.4. Its design is tied directly to kqueue, the BSD kernel event-notification facility that had recently made file, directory, and descriptor events available without busy polling.

使われ方

The command waits on one or more files or directories and exits when a requested event occurs. The manual gives examples such as watching a mailbox for writes, waiting for files to arrive in an incoming FTP directory, or using `-i` and `-t` so a script can tell which watched path changed or timed out.

Internally, `wait_on` uses kqueue's vnode notifications, including events for writes, extension, deletion, renames, link-count changes, attribute changes, and revocation. That makes it a compact bridge between shell scripting and kernel event delivery on systems with kqueue.

パッケージ好きにとっての重要性

This is a classic small Unix package: one command, one system primitive, and a clean scripting use case. It is historically interesting because it predates the later wave of cross-platform file-watcher tools and shows early BSD users solving shell automation without periodic `stat` polling.

タイムライン

• January 2002: `wait_on` was written under FreeBSD 4.4 by Andrew Stevenson.
• 2000s onward: the command remained useful as a shell-level wrapper around kqueue file and directory events.

Related projects

• The closest related primitive is kqueue itself. In the broader file-watching family, `wait_on` overlaps conceptually with inotify-based Linux tools and higher-level cross-platform watchers, but it stays intentionally close to the FreeBSD kernel interface.

ソース

• https://man.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2
• https://man.freebsd.org/cgi/man.cgi?query=wait_on
• https://www.freshports.org/sysutils/wait_on/