What is the purpose of -e in sed command?

Question

I can't find any documentation about the sed -e switch, for simple replace, do I need it?

e.g.

sed 's/foo/bar/'

VS

sed -e 's/foo/bar/'

Answer 1

This might work for you:

sed -e '/foo/i\bar' -e '/fred/a\barny' -e '/harry/c\potter' file

In each case the i(insert),a(append) and c(change) commands need to be terminated by a newline.

Normally commands can be separated by a ; e.g. /foo/d;/bar/d and grouped by {...} e.g. /foo/{h;d} but for the i,a,c commands the -e provides a way of separating the commands.

The alternative is to use the shell(bash) to insert a newline:

sed '/foo/i\bar'$'\n''/fred/a\barney'$'\n''/harry/c\potter' file

Answer 2

From the man page:

-e script, --expression=script

    add the script to the commands to be executed

So you can use multiple -e options to build up a script out of many parts.

$ sed -e "s/foo/bar/" -e "/FOO/d"

Would first replace foo with bar and then delete every line containing FOO.

Answer 3

-e script
--expression=script

Add the commands in script to the set of commands to be run while processing the input.