Number lines and write files, writes each FILE to standard output, with line numbers added to some or all of the lines.
If no input file (or '-' ) is given nl will read from standard input.

      nl [options]... [File]...


   -b STYLE
       Select the numbering style for lines in the body section of each logical page.
       When a line is not numbered, the current line number is not incremented,
       but the line number separator character is still prepended to the line.

       The styles are:
         'a'        Number all lines,
         't'        Number only nonempty lines (default for body),
         'n'        Do not number lines (default for header and footer),
         'pREGEXP'  Number only lines that contain a match for REGEXP.

   -d CD
       Set the section delimiter characters to CD; default is '\:'. If only C is given,
       the second remains ':'.  (Remember to protect '\' or other metacharacters
       from shell expansion with quotes or extra backslashes.)

   -f STYLE
       Analogous to '--body-numbering'.

   -h STYLE
       Analogous to '--body-numbering'.

   -i NUMBER
       Increment line numbers by NUMBER (default 1).

   -l NUMBER
       Consider NUMBER (default 1) consecutive empty lines to be one logical line
       for numbering, and only number the last one.
       Where fewer than NUMBER consecutive empty lines occur, do not number them.
       An empty line is one that contains no characters, not even spaces or tabs.

   -n FORMAT
       Select the line numbering format (default is 'rn'):

      'ln'     left justified, no leading zeros;
      'rn'     right justified, no leading zeros;
      'rz'     right justified, leading zeros.

       Do not reset the line number at the start of a logical page.

   -s STRING
       Separate the line number from the text line in the output with STRING
       (default is the TAB character).

   -v NUMBER
       Set the initial line number on each logical page to NUMBER (default 1).

   -w NUMBER
       Use NUMBER characters for line numbers e.g.000064 (default 6).

'nl' decomposes its input into (logical) pages; by default, the line number is reset to 1 at the top of each logical page.

'nl' treats all of the input files as a single document; it does not reset line numbers or logical pages between files.

A logical page consists of three sections: header, body, and footer. Any of the sections can be empty. Each can be numbered in a different style from the others.

The beginnings of the sections of logical pages are indicated in the input file by a line containing exactly one of these delimiter strings:
\:\:\: start of header;
\:\: start of body;
\: start of footer.
The two characters from which these strings are made can be changed from \ and : via options (see above), but the pattern and length of each string cannot be changed. A section delimiter is replaced by an empty line on output.

Any text that comes before the first section delimiter string in the input file is considered to be part of a body section, so 'nl' treats a file that contains no section delimiters as a single body section.

"Seek not the favor of the multitude; it is seldom got by honest and lawful means. But seek the testimony of few; and number not voices, but weigh them" ~ Immanuel Kant

Related linux commands

comm - Compare two sorted files line by line.
csplit - Split a file into context-determined pieces.
expand - Convert tabs to spaces.
seq - Print numeric sequences.
Equivalent Windows commands: FOR /F "skip=nlines" - Loop through items in a text file.

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