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NL(1P) POSIX Programmer's Manual NL(1P)

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

NAME
nl - line numbering filter

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

DESCRIPTION
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 char-
acters:

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

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

OPTIONS
The nl utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide-
lines. 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:

a
Number all lines.

t
Number only non-empty lines.

n
No line numbering.

pstring
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 num-
bered).

-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).

-p 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.

OPERANDS
The following operand shall be supported:

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

STDIN
The standard input is a text file that is used if no file operand is given.

INPUT FILES
The input file named by the file operand is a text file.

ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of nl:

LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions
volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization variables used to determine the values of locale categories.)

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

LC_COLLATE

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

LC_CTYPE
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).

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diagnostic messages written to stan-
dard error.

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

ASYNCHRONOUS EVENTS
Default.

STDOUT
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:

%6d When the rn format is used (the default; see -n).

%06d When the rz format is used.

%-6d When the ln format is used.

<empty>
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.

STDERR
The standard error shall be used only for diagnostic messages.

OUTPUT FILES
None.

EXTENDED DESCRIPTION
None.

EXIT STATUS
The following exit values shall be returned:

0 Successful completion.

>0 An error occurred.

CONSEQUENCES OF ERRORS
Default.

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 inter-
preter.

EXAMPLES
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.

RATIONALE
None.

FUTURE DIRECTIONS
None.