What are you trying to accomplish here?
Have you read man page of sed ?
The sed utility is a stream editor that reads one or more
text files, makes editing changes according to a script of
editing commands, and writes the results to standard output.
Since you are already using perl, why not just use perl to perform substitution (a lot of monks had already given out code) instead of *nix sed, then your code will be portable (across other OSes, like windows).
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Want more info? How to link or
or How to display code and escape characters
are good places to start.