SED - Numbering - Number each line of a file (simple left alignment)

Using a tab instead of space will preserve margins.

sed = filename | sed 'N;s/\n/\t/'

NOTE: = is used to number the line.

The expression \t is used to indicate a tab character (0x09) in the scripts.

Some versions of sed do not recognize the '\t' abbreviation, so when typing these scripts from the command line, you should press the TAB key instead.

'\t' is supported as a regular expression.

Example

Running that command again this file:

testfile

aaa
bbb
ccc

returns:

testfile

1	aaa
2	bbb
3	ccc