Linux Pocket Guide, 2nd Edition

Name

nl — stdin  stdout  - file  -- opt  --help  --version

Synopsis

nl [options] [files]

nl copies its files to standard output, prepending line numbers.

$ nl myfile
     1  Once upon a time, there was
     2  a little operating system named
     3  Linux, which everybody loved.

It’s more flexible than cat with its -n and -b options, providing an almost bizarre amount of control over the numbering. nl can be used in two ways: on ordinary text files, and on specially marked-up text files with predefined headers and footers.

Useful options

-b [a|t|n|p R ]	Prepend numbers to all lines (a), nonblank lines (t), no lines (n), or only lines that contain regular expression R. (Default=a)
-v N	Begin numbering with integer N. (Default=1)
-i N	Increment the number by N for each line, so for example, you could use odd numbers only (-i2) or even numbers only (-v2 -i2). (Default=1)
-n [ln|rn|rz]	Format numbers as left-justified (ln), right-justified (rn), or right-justified with leading zeroes (rz). (Default=ln)
-w N	Force the width of the number to be N columns. (Default=6)
-s S	Insert string S between the line number and the text. (Default=TAB)

Additionally, nl has the wacky ability to divide text files into virtual pages, each with a header, body, and footer with different numbering schemes. For this to work, however, you must insert nl-specific delimiter strings into the file, such as \:\:\: (start of header), \:\: (start of body), and \: (start of footer). Each must appear on a line by itself. Then ...