Files

Command	Effect
cat file	Prints the whole file.
less file	Pages through a file. / searches, q quits.
head -n 10 file	Prints the first 10 lines.
tail -n 10 file	Prints the last 10 lines.
tail -f file	Keeps printing new lines as the file grows, e.g. for logs.
touch file	Creates an empty file, or updates the timestamps of an existing one.
ln -s /path/to/target link	Creates a symbolic link link pointing to the target.
stat file	Size, permissions, owner and all timestamps.
file file	Detects the file type from the content.

Hard and symbolic links

flowchart LR
  sym[symlink] -->|path| name1[file.txt]
  name1 --> inode[(inode<br/>data)]
  hard[hardlink] --> inode

A symbolic link (ln -s) stores a path. It can point to directories and across filesystems, but breaks when the target is moved or deleted. A hard link (ln) is a second name for the same inode: the data stays until the last name is deleted, but it only works within one filesystem and not for directories.

Tip

Relative symlink targets are resolved from the link’s location, not from where you ran ln. When in doubt, use ln -sr target link, which calculates the relative path for you.