Files and directories

The difference between a symlink and a hard link, when to use which, broken links.

Navigation and files — ls, cd, cp, mv, rm, cat, less, head, tail, terminal copy-paste.

The ls command lists files and directories with permissions, owner, size and modification time, hidden ones too.

Creating directories: -p (with parents), -m (permissions right away), brace expansion, rmdir.

Full file information — size, permissions, owner, timestamps (atime/mtime/ctime), inode.

Figuring out what's inside a file (text, ELF, archive, image) by content, not by extension.

The cp command copies files and directories, with overwrite prompts, preserved permissions and times, recursively.

The mv command renames a file or directory and moves it elsewhere; it silently replaces an existing target.

The rm command deletes files and directories at once, with no trash; -i and -I ask first, -r removes a tree.

Symlinks (ln -s) and hard links: how they differ, when to use which, common mistakes with relative paths.

Splitting a path into a name and a directory, getting an absolute path; a script's own directory.

Finding files by name, size, time, permissions; acting on what's found.

Packs files into a compressed archive; an archive with no top directory dumps its files into the current directory.

Copies only the differences between trees; --delete mirrors the source into the destination, removing anything extra.

Incremental encrypted backups with snapshots; without the password the repository cannot be decrypted at all.

A version control system: who changed what in the files, how to get back a working version and exchange changes.