number

number [OPTION]... [FILE]...

-b STYLE, --body-numbering=STYLE
    Set numbering style for body lines. STYLE can be:
a: number all lines
t: number only nonempty lines (default)
n: number nothing
pREGEXP: number only lines that contain match REGEXP regular expression

-d DELIM, --field-separator=DELIM
    Use DELIM for field separator. Defaults to TAB.

-f, --first-page=NUMBER
    The first page number

-h, --header=STRING
    The header string

-i, --increment=NUMBER
    The increment number

-n FORMAT, --number-format=FORMAT
    Set number format. FORMAT can be:
ln: left aligned, no zeros
rn: right aligned, no zeros (default if -w not specified)
rz: right aligned, leading zeros (default if -w specified)

-p, --first-line-number=NUMBER
    The first line number.

-s STRING, --join-string=STRING
    String to append to (possible) line number. Defaults to TAB.

-v, --version
    Print version information and exit.

-w WIDTH, --number-width=WIDTH
    Use WIDTH columns for numbers. Default: 6

The number command adds line numbers to the lines of a specified file or standard input. It writes the numbered output to standard output. By default, it numbers all non-blank lines, but this behavior can be modified using options to number all lines or only lines matching a specific pattern. The output format and number alignment can also be customized.

number is useful for creating easily referenced copies of text files, adding line numbers to source code for debugging, or preparing documents for printing with line number references. It is often piped with other commands to add line numbers to their output, such as cat or grep.

The behavior of number can be significantly affected by locale settings, especially regarding character encoding and interpretation of whitespace. Regular expression matching can be complex, and it is important to understand the regular expression syntax used by your system.

number myfile.txt: Numbers all non-blank lines of 'myfile.txt' and prints to standard output.
number -b a myfile.txt: Numbers all lines (including blank lines) of 'myfile.txt'.
number -w 4 -n rz myfile.txt: Numbers lines with a width of 4, right-aligned with leading zeros.

The number command is part of the GNU coreutils, a package of essential file, text, and shell manipulation utilities common on Unix-like operating systems. Its development has evolved alongside the GNU project, aiming to provide a free and portable alternative to proprietary Unix tools. It's primarily used for adding sequential numbers to lines of text, often in preparation for printing or documentation.

cat(1), grep(1), nl(1)