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PROLOG
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.
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 characters:
┌───────────┬────────────┐
│ 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 POSIX.1‐2017, 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:
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 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).
-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 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:
LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of internationalization
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 standard 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 interpreter.
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.
SEE ALSO
pr
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The
original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .