Are there any differences between Gnu sed's "i text" and "i\ ...." commands? [duplicate]

Question

Below is an excerpt from Gnu sed's documentation at https://www.gnu.org/software/sed/manual/sed.html

i text
insert text before a line. This is a GNU extension to the
standard i command - see below for details.

i\
text
Immediately output the lines of text which follow this command.

The wording of these two syntaxes is quite different. In the past, I thought they have the exact same behavior and it's just the syntax is different. I did a bunch of experiment and all tests give the same result. I want to confirm, are there any differences between these two syntaxes? Thanks in advance.

Answer 1

The i text syntax is extension to the POSIX standard syntax for the i command in sed, provided as a convenience (as often is the case with GNU extension).

The standard i command looks like

i\
text

and POSIX documents this tersely with

Write text to standard output.

GNU sed provides the same syntactical convenience for the a and c commands as it does for i. The following is from the info sed documentation regarding the a command (GNU sed version 4.2.2):

As a GNU extension, if between the a and the newline there is other than a whitespace-\ sequence, then the text of this line, starting at the first non-whitespace character after the a, is taken as the first line of the TEXT block. (This enables a simplification in scripting a one-line add.) This extension also works with the i and c commands.

This implies that the two commands

i text

and

i\
text

are identical in GNU sed.