Adding line numbers to a file

The nl utility is useful for displaying line numbers in a file. This utility displays a file with line numbers added to each line. The utility breaks its input into logical pages. By default, the line number is reset to 1 at the top of each logical page. It treats all of the input files as a single document and does not reset line numbers or logical pages between files.

A logical page consists of three sections: header, body, and footer. Any of the sections can be empty. Each can be numbered in a different style from the others. An empty line of output replaces a section separator. Any text that comes before the first section separator string in the input file is considered to be part of a body section, so the nl utility treats a file that contains no section delimiters as a single body section.

Several options can be used to customize the output gained using this utility, and several of those options are covered in Table 4-16.

Table 4-16 Options Used with nl

Option

Use

-a

Numbers all lines.

-t

Numbers only nonempty lines.

-n

Does not number lines (the default for headers and footers).

-i

NUMBER

Increments line numbers by NUMBER with the default value of one.

-p

Does not reset line numbers at the start of each logical page.

-s

STRING

Adds the STRING after the added line number.

-v

NUMBER

Sets the initial line number on each logical page to NUMBER.

-w

NUMBER

Specifies the NUMBER of character spaces to reserve for line numbers. The default value is six.

Below is an example of the use the nl utility. In this example the nicks file is printed with a number corresponding to each line.

# nl nicks

1

Bammage

2

Rexmortis

3

Jackyl

4

Dragonstr

5

Alchemist

6

Just_joe

7

Johan

8

Sting

9

Dave

10

Thomas

11

Netchick

12

Netjunkie

13

Pri

14

Zaphod

15

Lordram

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