cat - concatenate files and print on the standard output

Options you will use

-n, --number

Number all output lines.

-b

Number non-empty output lines only.

-A, --show-all

Show non-printing characters, $ at line ends and ^I for tabs.

Gotchas

• cat file | grep x is a useless use of cat - grep x file is the same thing with one process fewer. shellcheck SC2002.

Taught in

• 1.5 Making things
• 1.7 Driving the shell: exit codes, chaining, redirection
• 2.21 Exec directives, environment and secrets
• 2.26 Hardening and cgroup limits
• 3.5 Reading top and vmstat, line by line
• 3.14 /proc: every process is a directory
• 4.1 Where things live
• 4.5 Permission bits and octal