The vim is the editor that is installed on every Linux system. It is the editor that the visudo, the crontab -e, and the many other tools open by default. It is the editor that the system administrator must know, because the alternative is the editor that may not be installed. The vim is modal:…
A system administrator edits configuration files. The edit is often a single line, a value, a directive. The editor should be simple, available, and fast. The nano is the editor that meets the criteria. It is installed by default on most distributions, it displays the keyboard shortcuts on the screen, and it does not require…
A file has content. The content can be small—a configuration line, a hostname—or large—a log file with millions of entries, a kernel source tree. The tools for reading the content are the ones that differ by the size and the purpose. The cat is for the small files and the concatenation. The less is for…
The rm command deletes files and directories. It is the most dangerous command in the shell because there is no trash bin, no undo, and no confirmation by default. The rmdir command deletes empty directories. The LFCS exam expects both commands to be automatic, and the exam tasks often require the cleanup of the files…
The mv command moves a file or directory from one location to another. It is also the command for renaming. On a Unix system, moving and renaming are the same operation: the file’s name changes, or its directory entry changes, or both. The mv command is the tool, and it is one of the most…
A watcher runs a side effect. The side effect may be asynchronous: a fetch that is in flight, a timer that is set, a subscription that is created. When the watched source changes before the side effect completes, the old side effect should be cancelled. The cleanup is the mechanism. The watch() and the watchEffect()…
A watcher reacts to a change. The default watcher reacts to the reference change: the ref’s value is replaced, or the reactive property is assigned. A nested mutation inside a reactive object does not change the reference, and the default watcher does not see it. The deep: true option makes the watcher traverse the object…
The watch() function requires the source to be named. The getter is written, the refs are listed, and the watcher knows exactly what it depends on. The watchEffect() is the opposite. It takes a function, runs it immediately, and tracks every reactive value the function reads. The dependency list is implicit, and it is derived…
A computed derives a value. A watcher reacts to a change. The distinction matters: the computed is for the derived state, and the watcher is for the side effect that runs when a reactive value changes. The watch() function is the Composition API’s mechanism for the side effects. It takes a source, a callback, and…
A computed property is a derived value. It reads from other reactive values and produces a new one. The template, the script, and the other computeds use it as if it were a plain value, and Vue ensures that it updates when its dependencies change. The computed() function is the Composition API’s mechanism for this….