nl man page


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

nl — line numbering filter


nl [-p] [-b type] [-d delim] [-f type] [-h type] [-i incr] [-l num]
    [-n format] [-s sep] [-v startnum] [-w width] [file]


The nl utility shall read lines from the named file or the standard input if no file is named and shall reproduce the lines to standard output. Lines shall be numbered on the left. Additional functionality may be provided in accordance with the command options in effect.

The nl utility views the text it reads in terms of logical pages. Line numbering shall be reset at the start of each logical page. A logical page consists of a header, a body, and a footer section. Empty sections are valid. Different line numbering options are independently available for header, body, and footer (for example, no numbering of header and footer lines while numbering blank lines only in the body).

The starts of logical page sections shall be signaled by input lines containing nothing but the following delimiter characters:

Line Start of
\:\:\: Header
\:\: Body
\: Footer

Unless otherwise specified, nl shall assume the text being read is in a single logical page body.


The nl utility shall conform to the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines. Only one file can be named.

The following options shall be supported:

-b type

Specify which logical page body lines shall be numbered. Recognized types and their meaning are:


Number all lines.


Number only non-empty lines.


No line numbering.


Number only lines that contain the basic regular expression specified in string.

The default type for logical page body shall be t (text lines numbered).

-d delim

Specify the delimiter characters that indicate the start of a logical page section. These can be changed from the default characters "\:" to two user-specified characters. If only one character is entered, the second character shall remain the default character ':'.

-f type

Specify the same as b type except for footer. The default for logical page footer shall be n (no lines numbered).

-h type

Specify the same as b type except for header. The default type for logical page header shall be n (no lines numbered).

-i incr

Specify the increment value used to number logical page lines. The default shall be 1.

-l num

Specify the number of blank lines to be considered as one. For example, -l 2 results in only the second adjacent blank line being numbered (if the appropriate -h a, -b a, or -f a option is set). The default shall be 1.

-n format

Specify the line numbering format. Recognized values are: ln, left justified, leading zeros suppressed; rn, right justified, leading zeros suppressed; rz, right justified, leading zeros kept. The default format shall be rn (right justified).


Specify that numbering should not be restarted at logical page delimiters.

-s sep

Specify the characters used in separating the line number and the corresponding text line. The default sep shall be a <tab>.

-v startnum

Specify the initial value used to number logical page lines. The default shall be 1.

-w width

Specify the number of characters to be used for the line number. The default width shall be 6.


The following operand shall be supported:


A pathname of a text file to be line-numbered.


The standard input shall be used if no file operand is specified, and shall be used if the file operand is '-' and the implementation treats the '-' as meaning standard input. Otherwise, the standard input shall not be used. See the Input Files section.

Input Files

The input file shall be a text file.

Environment Variables

The following environment variables shall affect the execution of nl:


Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2008, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)


If set to a non-empty string value, override the values of all the other internationalization variables.


Determine the locale for the behavior of ranges, equivalence classes, and multi-character collating elements within regular expressions.


Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments and input files), the behavior of character classes within regular expressions, and for deciding which characters are in character class graph (for the -b t, -f t, and -h t options).


Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.


Determine the location of message catalogs for the processing of LC_MESSAGES.

Asynchronous Events



The standard output shall be a text file in the following format:

"%s%s%s", <line number>, <separator>, <input line>

where <line number> is one of the following numeric formats:


When the rn format is used (the default; see -n).


When the rz format is used.


When the ln format is used.


When line numbers are suppressed for a portion of the page; the <separator> is also suppressed.

In the preceding list, the number 6 is the default width; the -w option can change this value.


The standard error shall be used only for diagnostic messages.

Output Files


Extended Description


Exit Status

The following exit values shall be returned:


Successful completion.


An error occurred.

Consequences of Errors


The following sections are informative.

Application Usage

In using the -d delim option, care should be taken to escape characters that have special meaning to the command interpreter.


The command:

nl -v 10 -i 10 -d \!+ file1

numbers file1 starting at line number 10 with an increment of 10. The logical page delimiter is "!+". Note that the '!' has to be escaped when using csh as a command interpreter because of its history substitution syntax. For ksh and sh the escape is not necessary, but does not do any harm.



Future Directions


See Also


The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines


2013 IEEE/The Open Group POSIX Programmer's Manual