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nl command in Linux with Examples

  • Difficulty Level : Medium
  • Last Updated : 05 Jan, 2021

Linux offers a wide range of commands for text formatting and editing. While editing a text file, you might want to display the lines with line numbers appended before them, and here comes the role-play of the nl command in Linux nl command is a Unix/Linux utility that is used for numbering lines, accepting input either from a file or from STDIN. It copies each specified file to STDOUT, with line numbers appended before the lines. 

Syntax:

nl [OPTION]... [FILE]...

Options:

-b NUMBER or -bNUMBER : used for numbering body lines
-i NUMBER or -iNUMBER : line number increment at each line
-n FORMAT or -nNUMBER : insert line numbers according to FORMAT
-v NUMBER or -vNUMBER : change first line number of the given input 
-l NUMBER or -lNUMBER : group of NUMBER empty lines are counted as one
-s STRING or -sSTRING : add any STRING after every logical line number
-w NUMBER or -wNUMBER : use different NUMBER columns for line numbers

Examples:

Note: Consider the following file as input in all the examples.



nl command in linux

1. To display a file with line numbers: Numbers all non-empty lines. 

$ nl geekfile.txt

To display a file with line numbers

2. To number all lines (including empty lines also): -b a option is used to number all lines whether empty or non-empty.

$ nl -b a geekfile.txt

To number all lines (including empty lines also)

3. Count multiple, consecutive, non-empty lines as one: -l option is used to count all non-empty lines as a single logical line to nl command. Linux considers NUMBER consecutive empty lines as a single logical line for numbering, and only numbers the last one. If any empty consecutive lines less than NUMBER occur, it will discard them.

$ nl -l 1 geekfile.txt 
## is same as 
## $ nl geekfile.txt

The example below considers 3 consecutive empty lines as a single logical line. 

$ nl -b a -l 3 geekfile.txt

Here, -b a option is used to consider all logical lines (whether empty or non-empty) as input to nl command.



Count multiple, consecutive, non-empty lines as one

4. Override default increment: The default increment pattern in Linux is 1. This can be changed using the -i option. The first line number is 1 and cannot be changed using -i.

$ nl -i 3 geekfile.txt
or
$ nl -i3 geekfile.txt

 Override default increment

5. To make the starting line number different: The default line number is 1. This can be changed using the -v option.

nl -v 4 geekfile.txt
or
nl -v4 geekfile.txt

To make the starting line number different:

6. Add a string literal after line numbers: Any STRING literal can be added after a line number using the -s option.

$ nl -s "..." geekfile.txt

Add a string literal after line numbers:

7. Change column for line numbers: Different columns can be used to display the file output using the -w option. The default column number is 1.

$ nl -w2 geekfile.txt
$ nl -w4 geekfile.txt
$ nl -w6 geekfile.txt
or
$ nl -w 2 geekfile.txt
$ nl -w 4 geekfile.txt
$ nl -w 6 geekfile.txt

Notice the change in column number (increase in indentation from left) in the example illustrated below.

Change column for line numbers

8. To number all logical lines that match the specified REGEX: -b pREGEXP option can be used to append line numbers before those lines only that match the given pattern. The following command will number those lines that begin with F.

$ nl -b pF geekfile.txt

To number all logical lines that match the specified REGEX

9. To print the lines using a different number format: The numbering formats can be specified using the -n option. The default numbering format is rn. The available options are:

  • ln -> left-justified, no leading zeros
  • rn -> right-justified, no leading zeros
  • rz -> right-justified with leading zeros
$ nl -n ln geekfile.txt
$ nl -n rn geekfile.txt
$ nl -n rz geekfile.txt

To print the lines using a different number format

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