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 reads lines from the named file or the standard input if no file is named and reproduces the lines to standard output. Lines are 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 is 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 are signalled by input lines containing nothing but the following delimiter characters:
Line Start of \:\:\: header \:\: body \: footer
Unless otherwise specified, nl assumes the text being read is in a single logical page body.
The nl utility supports the XBD specification, Utility Syntax Guidelines , except that the options can be intermingled with the optional file operand. Only one file can be named.
The following options are supported:
- -b type
- Specify which logical page body lines are to be numbered. Recognised 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 is 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 remains the default character ":".
- -f type
- Specify the same as b type except for footer. The default for logical page footer is n (no lines numbered).
- -h type
- Specify the same as b type except for header. The default type for logical page header is n (no lines numbered).
- -i incr
- Specify the increment value used to number logical page lines. The default is 1.
- -l num
- Specify the number of blank lines to be considered as one. For example, -l2 results in only the second adjacent blank line being numbered (if the appropriate h-a, -ba or -fa option is set). The default is 1.
- -n format
- Specify the line numbering format. Recognised values are: ln, left justified, leading zeros suppressed; rn, right justified, leading zeros suppressed; rz, right justified, leading zeros kept. The default format is 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 is a tab.
- -v startnum
- Specify the initial value used to number logical page lines. The default is 1.
- -w width
- Specify the number of characters to be used for the line number. The default width is 6.
The following operand is supported:
- A pathname of a text file to be line-numbered.
The standard input is a text file that is used if no file operand is given.
The input file named by the file operand is a text file.
The following environment variables affect the execution of nl:
- Provide a default value for the internationalisation variables that are unset or null. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined.
- If set to a non-empty string value, override the values of all the other internationalisation variables.
- Determine the locale for the behaviour 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- as opposed to multi-byte characters in arguments and input files), the behaviour of character classes within regular expressions, and for deciding which characters are in character class graph (for the b-t, -ft and -ht 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 catalogues for the processing of LC_MESSAGES .
The standard output is 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.
Used only for diagnostic messages.
The following exit values are returned:
- Successful completion.
- An error occurred.
In using the -d delim option, care should be taken to escape characters that have special meaning to the command interpreter.
The command:will number 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 will not do any harm.
nl -v 10 -i 10 -d \!+ file1
The intermingling of the file operand with the options is an obsolescent feature that will be removed from a future issue.