GNU implementation of the POSIX stream editor `sed'.

Sed (streams editor) isn't really a true text editor or text
processor. Instead, it is used to filter text, i.e., it takes text
input and performs some operation (or set of operations) on it and
outputs the modified text. Sed is typically used for extracting part
of a file using pattern matching or substituting multiple occurrences
of a string within a file.