These docs are under active development and cover the v0.20 Kobicha security model.
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nl

nl prints a file with its lines numbered. cat -n also numbers lines; nl is the command for when you need control over the numbering — which lines count, how the number looks, where it restarts.

nl [options] [file...]

$ nl chapter.txt
     1  Once the system is installed,
     2  the first boot brings up
       
     3  the configuration service.

Which lines get a number

By default nl numbers only the non-empty lines. -b sets the rule:

-b STYLE Numbers…
-b a every line.
-b t only non-empty lines. This is the default.
-b n no lines.
-b pBRE only lines that match the basic regular expression BRE.
Option Effect
-b, --body-numbering=STYLE The numbering rule, as above.
-l, --join-blank-lines=N Count a run of N blank lines as one numbered line.

How the number looks

Option Effect
-n, --number-format=FORMAT ln = left-justified; rn = right-justified; rz = right-justified with leading zeros.
-w, --number-width=N Use N columns for the number.
-s, --number-separator=STRING Put STRING between the number and the line text.
-v, --starting-line-number=N Start counting from N.
-i, --line-increment=N Increase the number by N at each counted line.

Logical pages

nl can treat one file as a sequence of logical pages, each with a header, a body, and a footer, and number the three parts by different rules. Pages are separated by special delimiter lines in the input.

Option Effect
-h, --header-numbering=STYLE Numbering style for header sections.
-f, --footer-numbering=STYLE Numbering style for footer sections.
-d, --section-delimiter=CC The characters that mark a section boundary in the input.
-p, --no-renumber Do not reset the line number at the start of each logical page.

The styles for -h and -f are the same a / t / n / pBRE set as -b. For an ordinary file with no delimiter lines, the whole file is one body and only -b matters.

Exit status

Code Meaning
0 Success.
1 A file could not be read, or an option value was invalid.

See also