Programming :: Prevent Sed From Replacing With Newline

I'm writing a script to replace some text that exists in about 50 .lex, .y, and .cc source code files, sometimes more than once in a file. Sometimes the text is in a multiline C comment, and other times it's within a multiline C string.

I use sed to grab the start and end of each line and wrap the new text in the old whitespace and/or quotes and Problem is, sed is changing the characters into a newline.

Is there a way to tell sed to not process escape sequences? I tried using several variations of

Code:

To no avail. Or could it be bash?

I would give up on the script and do it by hand, but this is something that I must do from time to time.

Here's the function which replaces the first occurrence found:

Code:

When $post is printed by echo, it shows the - but by the time the file is on disk, it becomes a newline. What should I do to ensure that it stays as the characters ?