The general format of a sed editing command is:
[address1[,address2]] function [arguments]
An address is a parameter which tells sed which lines to
apply the function to. Addresses may be line numbers or regular
expressions. If two addresses are specified, sed applies
the function to all the lines in the range from address1
to address2. You can omit one or both addresses; in the
absence of an address sed applies the function to every
line that it reads. For example, the following script turns every
occurrence of ``red'' into ``blue'' throughout a file:
The function determines the operation that sed carries out on the matching line. A function is always required in a command, but arguments are optional for some functions.
Any number of blanks or tabs can separate the addresses from the function, and tab characters and spaces at the beginning of lines are ignored.