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nl - line numbering filter
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 the file argument is omitted, applies a configurable line numbering fil‐ ter operation and writes the result to the standard output. The nl utility treats the text it reads in terms of logical pages. Unless specified otherwise, 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 sections. The starts of logical page sections are signalled by input lines contain‐ ing nothing but one of the following sequences of delimiter characters: Line Start of \:\:\: header \:\: body \: footer If the input does not contain any logical page section signalling direc‐ tives, the text being read is assumed to consist of a single logical page body. The following options are available: -b type Specify the logical page body lines to be numbered. Recog‐ nized type arguments are: a Number all lines. t Number only non-empty lines. n No line numbering. pexpr Number only those lines that contain the basic regu‐ lar expression specified by expr. The default type for logical page body lines is t. -d delim Specify the delimiter characters used to indicate the start of a logical page section in the input file. At most two characters may be specified; if only one character is speci‐ fied, the first character is replaced and the second charac‐ ter remains unchanged. The default delim characters are “\:”. -f type Specify the same as -b type except for logical page footer lines. The default type for logical page footer lines is n. -h type Specify the same as -b type except for logical page header lines. The default type for logical page header lines is n. -i incr Specify the increment value used to number logical page lines. The default incr value is 1. -l num If numbering of all lines is specified for the current logi‐ cal section using the corresponding -b a, -f a or -h a option, specify the number of adjacent blank lines to be considered as one. For example, -l 2 results in only the second adjacent blank line being numbered. The default num value is 1. -n format Specify the line numbering output format. Recognized format arguments are: ln Left justified. rn Right justified, leading zeros suppressed. rz Right justified, leading zeros kept. The default format is rn. -p Specify that line numbering should not be restarted at logi‐ cal page delimiters. -s sep Specify the characters used in separating the line number and the corresponding text line. The default sep setting is a single tab character. -v startnum Specify the initial value used to number logical page lines; see also the description of the -p option. The default startnum value is 1. -w width Specify the number of characters to be occupied by the line number; in case the width is insufficient to hold the line number, it will be truncated to its width least significant digits. The default width is 6.
The LANG, LC_ALL, LC_CTYPE and LC_COLLATE environment variables affect the execution of nl as described in environ(7). The nl utility exits 0 on success, and >0 if an error occurs. jot(1), pr(1)
The nl utility conforms to IEEE Std 1003.1-2001 (“POSIX.1”).
The nl utility first appeared in AT&T System V.2 UNIX.
Input lines are limited to LINE_MAX (2048) bytes in length.