nl (Number Lines)

Explanation

The nl command reads lines from a file and outputs them with line numbers added. While cat -n can also number lines, nl provides more advanced formatting options, such as numbering only non-empty lines (the default behavior) or using specific numbering styles.

Basic Syntax

nl [OPTION]... [FILE]...

Common Flags and Options

Flag	Description
-b, --body-numbering=STYLE	Use STYLE for numbering body lines (e.g., a for all, t for non-empty (default)).
-n, --number-format=FORMAT	Insert line numbers according to FORMAT (ln, rn, rz).
-w, --number-width=NUMBER	Use NUMBER columns for line numbers.
-s, --number-separator=STRING	Add STRING after (possible) line number.

Real-world Examples

1. Number non-empty lines in a file (default):

   nl script.sh

2. Number all lines, including empty ones:

   nl -b a script.sh

3. Format line numbers with leading zeros:

   nl -n rz script.sh