Add line numbers to nonblank lines of text in a file and write to standard output.
nl [options] [file]
-ba numbers all lines.
-bt numbers text lines only (the default).
-sc separates text from line numbers with the character c (the default is tab).
-wn uses n columns to show the line numbers.
The nl command adds a line number to each nonblank line of text from a file and writes the lines to standard output. Suppose the file sample.txt has the following lines:
A line followed by a blank line and then another non-blank line.
The nl command applied to this file produces the following result:
nl sample.txt 1 A line followed by a blank line and 2 then another non-blank line.