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1 Introduction
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‘sed’ is a stream editor.  A stream editor is used to perform basic text
transformations on an input stream (a file or input from a pipeline).
While in some ways similar to an editor which permits scripted edits
(such as ‘ed’), ‘sed’ works by making only one pass over the input(s),
and is consequently more efficient.  But it is ‘sed’'s ability to filter
text in a pipeline which particularly distinguishes it from other types
of editors.